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1980 450SL named Freya. 202,000mi
574 Posts
Discussion Starter · #1 · (Edited)
EDIT (Nov 26) due to the length of the posts in this thread, POST 22 contains a table of contents and bibliography to help readers find specific information.

POST 23 is a "Cliff's Notes" summary of the entire thread.

It is my intention to make this thread a "follow along as I figure this out", through the process of diagnosing and repairing my 450SL. I am now at a point of some "hard facts" to relate, and a point where I think I am now making progress.

Nevertheless, please comment and add advice as I am "learning as I go".


The subject vehicle is a 1980 450SL with 199,500 miles on it. I bought it 14 years ago with 121,000 miles. As I now work from home (since 2009) I drive it less than 5000 miles a year.

The vehicle has been "running worse" for some time. About 3 months ago I paid my mechanic roughly $700 to tune it up and get it running better. Nevertheless, it FAILED smog last week. My mechanic, and the smog guy, both indicated that the engine was week, and possibly needed major mechanics, possibly even a valve job. Mike at Johann's is INCREDIBLY honest and kind, and he indicated that I could be looking at "$3000 to $5000" - he suggested that I retire the car, possibly hold it somewhere until it improved in value. But he said that it could become a money pit.

Well, Im NOT going to put 5K into this car right now, and I don't want to get another car, plus I don't see the point in trying to sell a car that won't pass smog in California.

Therefore I have taken matters into my own hands, and I'm going to work the problem out myself (with the kind help of the members of this forum) :smile

Before I decide to retire the car, I wanted to spend some time with it on my own, and potentially make it "my project".


I have a couple other threads:


Aluminum Heads in a 450SL? OOOPS!!

Fuel Accumulator Question and Notes

But I intend THIS thread to be the main diary of the diagnosis and repair process. I may start some other threads for the express purpose of a tangential question, such as the fuel accumulator thread noted above.


The car failed smog, has a rough idle, and when my mechanic replaced the plugs a couple months ago, I noted that plug ONE and to a lesser extent plug FIVE were heavy in carbon deposits. Plug ONE was just solid black with carbon. I've run several tanks with Techron Injector Cleaner over the previous month in freeway driving.

When the smog guy (a friend of the mechanic) said there was no way the car could pass, my mechanic also stated that the engine was weak, and could be a very expensive repair (i.e. valve job).

Since I don't actually need a car that often, and I am a ZipCar member, I can take a little time to see if I can solve the problem. However, I don't have a garage where I can do a total teardown, so for me, a head R&R is out of the question.

The first step, therefore, is determining if I can actually handle bringing the car back to proper operation including of course passing smog. Simply, if it needs a head R&R I'll just store the car, but if the engine is strong, then I can move forward and fully diagnose and repair the vehicle.


I've never done a compression test before, but it seemed to me the most logical way to proceed - if the car fails, I abandon it for the time being. If it passes, then the remaining repairs should be easily within my grasp both financially and from a skill point of view.

I watched a couple YouTube videos, and I'll suggest THIS ONE as the most comprehensive and watchable:

I then went to Harbor Freight, and purchased a couple tools for my diagnostics. First, this compression gauge:

Quick-Connect Compression Tester

$30 with tax - note that it is a little more expensive than some of their gauges, but there is no sense trying to save $6 (remember, I am trying to save THOUSANDS by properly diagnosing the car). This meter has a quick disconnect that allow you to easily thread into the spark plug hole, and then connect the meter. the meter is well made, as are the fittings and it worked well as I discuss below.

The second tool I bought there was a multimeter with duty cycle, which I will discuss in diagnosis part two.


As I discuss in the thread "Holy Smoke!", as part of my trip to Harbor Freight, I planed on using Sea Foam on the engine. I wanted the engine as clean as possible before compression testing. As noted in that thread, the Sea Foam application made a big difference in the way the car operated (or at least it seemed that way. LOL - never discount the placebo effect). Yesterday and today, I made some adjustments to idle and mixture (I'll discuss these adjustments in part TWO below).

I enlisted the help of a girlfriend of mine to turn over the ignition and/or hold the light while I was under the hood. On my way to pick her up, I made additional notes for diagnosis that will be discussed below in part two.


Picking up my assistant allowed me to get the engine heat soaked, an important first step in the compression test.

Once back home, I removed the FUEL RELAY (near the fuse box) then turned the ignition to clear any gas out of the system. The car sputtered a bit, never really starting (possible fuel accumulator or pressure leak - pressure leak will be a later part of the diag).

Then I removed the air filter assembly, and removed all the spark plugs. I placed each plug in a flat piece of cardboard with number to indicate where each plug came from.

As you can see, all the plugs have light carbon, but plug ONE is just covered in it. These plugs have less than 500 miles on them.



The carbon on plug ONE is dry and soft/flakey. The other plugs are fairly clean - the electron being whitish, and some carbon (harder) around the ring.


I am a pretty happy guy today! :grin I was so happy with the compression results that I only did a "dry" test (no squirt of oil).

I connected the hose carefully to each plug hole, then attached the meter to the hose.

I placed a distributor wrench in the AIR SENSOR to hold it open to make certain there was no air blockage. I also had my assistant hold down the accelerator pedal to the floor.

I then had her turn over the ignition 8 revolutions. I noted the "first puff", and also the final compression figure. I did cylinder ONE twice, and cylinder FIVE three times beaus sit was the weakest cylinder. I wrote the figures down on this spreadsheet:

YES!!!!! The "problem" cylinder (the one missing) had good compression, and the plug from the weakest cylinder indicated normal deposits (similar to the other 6 plugs).


1 - 143
2 - 145
3 - 147
4 - 145
5 - 135
6 - 145
7 - 142
8 - 150

Average: 144

Median: 145

Worst cylinder is 93% of median. Best cylinder is 103.4% of median.

I was pretty exstatic when I saw the results for cylinder ONE. That $30 compression tested saved me $5000.

I replaced all the plugs, and I noticed the rubber strain relief on the #1 and #2 wires was split:

# 1 Wire

#2 Wire

This doesn't look like it should be an actual problem as the high voltage insulation ceramic is intact (the red part). These were OEM wires that I installed about 50K miles ago. They seem to have proper continuity/resistance, but I am going to study them in more detail in a future diagnosis. (i.e. I have not yet ruled them out as a problem).

After reassembling the car, and re-inserting the fuel pump relay, the car started fine, albeit with the run problems I am working on correcting.

Interesting side note: I was able to remove the Fuel Relay without removing the under-dash cover - but I couldn't get it back i, and had to remove the under dash panel to reinsure the relay.



1980 450SL named Freya. 202,000mi
574 Posts
Discussion Starter · #2 · (Edited)


I actually conducted parts of the "part two" diagnosis prior to the compression test, but technically the compression test should be the "first" in series. Some of these other tests encouraged me to conduct the compression as I felt the problem was reasonably elsewhere.

First off, I wanted to try two last-ditch efforts. Sea Foam and Duty Cycle.

On the subject of duty cycle - when I took the car to get smogged, the smog guy attempted to adjust it to get it to pass. The car still failed (the guy was nice and did not charge me at all). Unfortunately, his adjustments also made the car practically UN-DRIVEABLE. Seriously, I had to keep my right foot on the accelerator pedal at all time to keep it from stalling.

I went to Harbor Freight, and picked up this Digital Multimeter with Duty Cycle:

5-in-1 Digital Multimeter

It was on sale for $49.95. WOW, gotta love Harbor Freight. This meter may be overkill for some of you, but the meter is something I use for other work I do (and I have a bunch of meters, LOL so an excuse to buy another one...) This meter is pretty nice, it has a backlight and a number of very useful features for me for other applications.

At any rate, I set it to duty cycle, and connected the BLACK lead to PIN 2 (ground), and the RED lead to PIN 3 (lambda duty cycle) of the X11 connector:

I then used a 3mm Hex wrench to adjust the MIXTURE on the fuel distributor.


My duty cycle read 59.7% after the car was fully warm. And it wasn't moving AT ALL when I attempted to adjust the mixture control on the fuel distributor. However, I WAS able to get the car to run without sputtering and stalling.

Well, I've read enough to know that if the duty cycle remains static like that, it indicates a bad O2 sensor (or possibly a bad ECM). HA! A failed O2 sensor will also result in a smog test failure. I'm ON TO SOMETHING!!

For a pretty good explanation of the Lambda system, see this link:


EDIT (Oct 26th) WARNING! The KE3-JETRONIC page linked above has several aspects that DO NOT APPLY to 1980 thru 85 K-Jet systems, as I discovered (see repair part three below) I am leaving the link here as some of the info is useful, but the target duty cycles are much different.


Okay, so I know that at least the O2 sensor is dead. With the mixture and idle adjusted so the car at least "seems" to run, let's try Sea Foam!!! FWIW, I did the Sea Foam just prior to the compression test, as I wanted to get the engine as clean as possible prior to compression testing.

I detail this more in the "Holy Smoke" thread, but basically, after bringing the car to operating temperature, I poured an ENTIRE bottle of SeaFoam down the air sensor. I poured very slowly at first, holding the throttle linkage around 2000 RPM, then dumped that last 4 Oz or so all at once (nearly, but didn't quite kill the engine.) After waiting 25 minutes, I took the car on a "spirited drive" with smoke billowing out. The cars was at least appearing to run better, and had lost of "go" on the freeway.


Before compression testing today (see part one), I needed to bring the car up to a "heat soaked" condition. I did this on my drive to pick up my assistant.

Since I was doing a cold start, I turned on the voice dictation on my iPhone, and dictated the following notes as I started the car and drove, to help me remember the minutes of the various problems:

NOTE: I know from a previous diagnosis that the heating element in the WUR is open, thus not functional. Only engine heat affects the WUR.

450 SL notes

Today Cold initial start was fine however engine soon sputtered and died. after restarting I had to hold the idle speed up to around 2000 manually by pressing the gas pedal.

As I drove and the temperature started to come up the car began running smoother including an idle with the temperature gauge reading approximately 60 and in DRIVE the idle is a little bit under 1000 according to the dashboard tach.

Driving and accelerating seem to be operating just fine

Idle now decreased to 900 seems to be a relatively smooth but with an occasional miss

Once I got the engine up to operating temperature of 85 I adjusted the idle speed screw to reduce the idle slightly to approximately 800 per the dashboard tach, while in PARK/NEUTRAL.

Putting car in DRIVE it drop downs to about 600 and the engine stalled I readjusted the screw for faster idle (¾ turn).

Note: there is about a 200 to 300 RPM drop between Drive and neutral. Must check to see if idle RPM spec of 650 is drive or neutral.

At Candy's I shut off engine for 7 minutes to assess the hot start problem. It would start then die.
TEST (see the fuel accumulator thread): With engine off, place PRNDL in D, then turn ignition to START for 10 seconds to see if fuel accumulator fills.

Okay after attempting to run fuel pump for 10 seconds, hot start problem still exists (does this seem to rule out the fuel accumulator?)


Now as engine heats up above 85C, I am dropping down to about 700 RPM. OIL pressure's a little bit above 1.

I'm at a stoplight and the idle does continuously drop down just a little bit, until the car stalls.

Alright more driving and it is now overheating (95 C) and stalling. Idle in neutral drops under under 600 as engine over heats - Idle slowly drop and stalls.

Okay, with the engine overheating I am once again getting backfire through the exhaust on deceleration.

Okay now with the engine heats out but not exactly overheating still having a problem with Idol I'm thinking that this has to do with the warm-up regulator system and that because it doesn't have a heating element it's actually finally getting to the correct control pressure but the engine is not adjusted to compensate at the correct total pressure

Okay I think I figured out the warm-up regulator issue I have reason so as the regulator starts to go over temperature, this increases the control pressure so that the mixture becomes lean until the engine stalls and must be stalling from starvation in addition the leaner mixture is contributing to the overheat problem

So that was all on the drive to Candy's and the way home. As I think about the WUR, I realize that without the heating element, it's dependent entirely on engine heat for altering the control pressure. As it happens, when I first determined that the heating element was open (like, a year ago) I HAD been thinking " whatever, it's just for warm up".

OH SO WRONG I WAS. In my opinion the "Warm Up Regulator" is poorly named. It SHOULD be called the CONTROL PRESSURE REGULATOR.


My recent research has shown that it is so integral to the proper fuel pressure operation, implying that it's just about cold operation is misleading!! As I am currently thinking in the present diagnosis, the fact that idle drops as the car heats indicates that the control pressures are all whacked out - if you adjust for nominal engine temp, the control pressures will be totally wrong if it heats up further - this is because with no heating element, the WUR is ONLY responding to engine temp - WITH the heating element (I believe)it should become stable at a temp higher than engine temp. (please correct me if I am wrong in this assumption).

EDIT NOV 26: I'll correct myself on this point. The idle speed decline when the car overheats is due to the Idle Aux Air Valve closing at too hot a temperature. The WUR does have some effect on idle, but the AAV is the real culprit here. Once at engine temp, the WUR is fairly stable. The real symptom here was that the WUR with a failed heater would cause enrichment longer than needed. It is also possible that my WUR was not providing correct pressure, though I did not specifically test this.


Okay, so thus far the mandatory replacements are:

Oxygen Sensor
Warm Up Regulator

However, the O2 sensor and the WUR do not explain the reason that Plug ONE is misfiring and coated totally in carbon (while the other plugs indicate (relatively) normal firing).

Plug ONE will be covered in PART THREE, which I have not completed yet. Part Three will center on fuel injectors and the ignition system,

1980 450SL named Freya. 202,000mi
574 Posts
Discussion Starter · #3 ·

I Purchased a rebuilt WUR from SpecialTAuto for $240

Warm up regulator-Special T Auto has the correct warm up regulator and warm up regulators for all cars - The De Lorean Parts Specialists

And From AutohauzAZ (my go-to parts supplier) I bought:

The O2 sensor we've discussed. The smog guy said my Fuel Cap was bad - odd since it was only a couple years old (California Emissions are STRICT), nevertheless, might as well get that now.

I suspect the #1 fuel injector, but considering AutoHausAZ has them for $30 each, it makes sense to replace all 8. It is important to replace the seals too, with the injectors. Interestingly, the nylon holder with Oring is actually than the Oring by itself.

My blue ballast resistor has cracks in the ceramic casing. It is still a functional resistor (the internal element is a coil of wire), but I've been wanting to replace it for some time, even though it should have no effect on operation.

The Aux Air Valve gasket is for some of the troubleshooting I am planning - and it will involve removing the AAV for cleaning, so I'll need that gasket.

And my rubber mounts for the air cleaner have pretty much failed.

So the total parts bill right now is $579 - small price if it fully fixes the problems (though I don't count on it).


If this round, with the injectors, does not bring the car up to good operating condition, the NEXT step is:


Distributor cap, Rotor, and a new set of Spark Plug Wires.

Estimated cost: $150.


Fuel Filter, Check Valve, (maybe accumulator, depending on pending tests).

Estimated cost: $30 to $130 (depending on accumulator or no accumulator)

And then a "more final" round is to remove the intake manifold and replace all the intake gaskets - those 8 little rubber rings, the throttle gasket, etc etc. These gaskets all together will only be $60 - but, wow, what a pain. Hence saving for "last".


Todays compression test took about 6 hours of my time (including picking up my friend).

I expect the R&R of the parts I bought today to take about 3 hours. The ignition and fuel stuff should be about 2 hours. the intake manifold? Yikes. I'm gonna guess 10 to 12 hours.

All told, I see this total project costing about $900 to $1000 in parts, and about 25 to 30 hours of my time. But my expectation is to have a car that runs very well.

Till part three...... :wink


1980 450SL named Freya. 202,000mi
574 Posts
Discussion Starter · #4 ·


I received my parts from AUtohausAZ promptly as usual. For the WUR, SpecialTAuto requires that you send in the core FIRST with a money order - so I shipped it to him overnight USPS, and he shipped it back out the same day (priority at no additional cost), so I got it Saturday. The biggest drag with this is that from Weds to Sat., by car was inoperable with no WUR. I wish he offered a core charge and then refund, but he's a one man operation, and his prices are the best so I can't really argue. The rebuilt WUR I received was an excellent rebuild (i.e. like a new part).

I installed the rebuilt WUR, and discovered that the electrical connector's wire was broken. The connector seems hard to come by, so I took the old connector, and used a Dremel to open up the side just enough to allow me to solder on a couple new leads. I closed it up using heat-shrink tubing, and attached my leads to the old leads in the wiring harness.

I also replaced the FUEL INJECTOR, including the seal and the plastic seat and O ring for Cylinder number ONE only (as you may recall, I am particularly focused on cylinder #1 as the plug was completely black with carbon).

The first thing I noticed with the new WUR installed was that the idle was suddenly much higher than before - I backed off the mixture a bit, and did a test drive (I have not installed the new O2 sensor yet). While the car drives "okay" on the freeway, the idle under load still creeps down to a stall.

The next item to install was the O2 sensor. I found a great DIY garage here in Los Angeles:

Your Dream Garage

For $25/hour you get a lift and all the tools you need (almost). While I was at it, I did an Oil & Filter change with two bottles Auto-RX for an internal cleaning as well.

The O2 sensor was replaced more-or-less without incident, though the one tool the DIY garage did not have was a stripper/crimper (and I left mine at home), but I managed using a pair of ***** to strip the lead, and a vice-grip to crimp it.

When I started the engine after installing the O2 sensor, I noticed an IMMEDIATE improvement - in fact, for a few minutes it seemed that the missing went away. Also, checking the duty cycle, it was clear the Lambda system was now functioning, as the duty cycle was about 45% and moving up and down as it should.

However, the miss was in fact still present, and obvious once the engine was warm and idle dropped down to around 800.

I also checked the vacuum lines, and all are as they should be (note that I re-did all vacuum lines a couple years ago).


WUR, O2 sensor and #1 injector replaced. Attempts made at adjusting mixture and idle screw. Vacuum lines checked for correctness.


  • Lambda system now seems functional.
  • The overheat problem seems to be gone (though that may be due to cooler weather, and that I have not been driving the same). Nevertheless the car seems to be running cooler.
  • Cold starts are way better. Warm starts *seem* to be better/easier - but there is still a warm stall and idle issue per below.


  • There is still a miss happening, in fact, it seems like it may be WORSE than before. I am still assuming that it is cylinder #1 .
  • After driving and coming to a stop (such as at a stop light) with the car in D, the car idles around 700 but SLOWLY decreases until the car stalls (under 600).
  • With the car in neutral, if you rev engine to 3000 for 30 to 40 seconds, then release the pedal, the car will idle at between 1100 and 900 (seems inconsistent). My thought here is that revving the engine to 3K in neutral allows the engine to "clear up" a rich-foul situation.
  • Putting car back in gear brings the idle down to 700 to 800, and then it slowly decreases until it stalls.
  • The idle is "loping".
  • Duty cycle is about 45% at idle. Attempting to lean the mixture screw (to get the duty cycle up to 50%) results in the engine stalling.


I tested the spark plug wires with an ohmmeter and got about 1.5 kOhms which is within spec. The wires are an OE Bosch set that I had installed about 65K miles ago. They seem to be in fine condition except for the strain relief in a couple that I noted in the first post. While they seem okay I am considering replacing them.

I am also considering replacing the cap and rotor (which was last replaced with the wires, but has been cleaned recently).

As we know the compression is good, and we have replaced the injector for #1 , the plug wires and cap/rotor are the next most logical cause of the consistent misfire in a specific cylinder.

Before I do that though, I am going to replace the #1 plug. While I did clean it, I never fully got rid of the black on the insulator and I'm concerned the carbon is causing a short and weak spark. Secondly, as this is the plug that is under the radiator reservoir, I am concerned that I may have cross-threaded it and that is resulting in lower than ideal compression (though I'm not "hearing" that under the hood).

Thus, a new plug may actually correct the misfire, now that the injector is replaced, and the mixture is going to be more correct with the new WUR and O2 sensor (this is only a theory at this point).

Because the misfire seems to be a rich misfire in only one cylinder, I am discounting the fuel distributor. I am also (at present) not looking at the possible issues with the fuel accumulator and idle Aux Air as those should affect all cylinders (Right?!?!) I want to solve the single cylinder misfire FIRST.


First off tomorrow I'm going to pick up a new W9DC plug and put it into cylinder 1, taking extra great care to make sure it is not cross-threaded. If this does not solve the misfire, then I see no alternative but to order the full plug wire set, cap, and rotor from AutohausAZ.

1980 450SL named Freya. 202,000mi
574 Posts
Discussion Starter · #5 · (Edited)


Today I did minor work on Freya (my name for my 1980 450SL - Freya is the norse goddess of love and war).


First of all, I replaced plug #1 with a brand-new plug.

As you may recall, all plugs were replaced less than 1000 miles ago, and when doing the compression test, plug #1 was totally fouled with carbon. Despite having attempted to clean the fouled plug, I just couldn't get all the carbon off the insulator. Interestingly, when I removed this plug today, it was in fact CLEANER than when I put it back in, which indicates to me that the #1 injector which I replaced really was the main cause of the issue.

With the new plug in place, the serious constant misfire is now GONE. There are still some intermittent and occasional misfires that I have yet to deal with.


In doing this, the new plug happened to be a WR9DC - this is the RESISTOR version, as the parts shop didn't have the non-resistor W9DC. As it happens, I discovered that ALL the plugs in my car are the resistor version. My mechanic replaced all the plugs they used the resistor version, as Bosch no longer makes the non-resistor type. As I have OEM plug wires (I believe they are Bosch, installed around 2003), I believe that using the resistor version of plugs may be a contributing problem. These are jumping up on my list of things to replace.


As noted in This Thread on Spark Plug Wires, I intend to replace the spark plug wires, cap, rotor (and now also the plugs) in a future round of engine maintenance. At the moment, I'm not certain it's critical to smog check which is the first priority at the moment.

When I DO replace these ignition parts:

Wires: 77-80 450SL plug wire set

Cap and Rotor: Bosch

Plugs: Non-resistor. W9DC if I can get them, otherwise another equivalent non-resistor plug such as NGK.


The BLUE ignition resistor had a ceramic casing that was completely cracked and crumbling. While the resistor coil inside was still perfectly operable, I opted to replace this part ($21 at AutoHausAZ) add I didn't want to deal with a failure down the road. It shouldn't have any effect on performance.


Some of the vacuum lines were fitting a bit loose - as a temporary measure, I used some permatex non-hardening gasket sealant on the two loose connections. Nevertheless, I think looking at the vacuum components should be on the list of things to do in the near future (like later this week).


Well, embarrassingly, I have reason to believe when I was testing the Lambda system after replacing the O2 sensor, I connected my duty meter to the wrong pins on the X11 connector. It should be black to 2 and red to 3, but I think I did black to 3 and red to 4. Needless to say, this gave me meaningless information.

TODAY, I correctly connected black to 2 and red to 3, and found the duty cycle varying between 59% and 62%. And it stayed there regardless of how I adjusted the mixture on the fuel distributor. In otherwords, it seems like the system is operating in OPEN LOOP MODE even after the engine is fully warm.

UGH. So, there is more troubleshooting to go on the mixture/Lambda system.

EDIT:I since discovered that the pin 3 of the x11 connection can NOT be read directly with a standard duty cycle meter.

I did make some adjustments to the mixture and idle screw to get the car running better. With the injector leak and fouled plug replaced, I am able to get a mixture and idle setting where the car mostly does not stall. In fact, after a short freeway drive tonight, it was running SO much better, I decided to run yet another pass of Sea Foam.


As I did in the thread HOLY SMOKE!, I decided to run another pass of sea foam on the car, now that the injector and fouled plug were replace, and see where that leaves us.

I put about 8 Oz in the tank with 5 gal of premium, and I poured a whole can down the throttle as before. I let it sit about 20 minutes, and then hopped on the freeway - and at 4AM I was pretty much able to floor it.

One thing I have to do is fix the belt tension. I had new belts put on, but they squeal at 4000 RPM. UGH!

I drove about 25 miles, pegging the speedometer when I could. It ran very well and much MUCH smoother than it has in years.


The hot start problem and hot restart then stall problem seems to be gone completely since the injector is replaced - this (and the fact the #1 plug was cleaner today than before the injector was replaced) indicated to me that the problem was CENTERED around the #1 injector leaking. This leaking injector in turn caused other issues such as the fouled plug, which subsequently needed to be addressed.

BUT - idle still is not perfect.


Idle is ALL OVER THE PLACE. (numbers below based on dashboard tach).

In DRIVE, after driving on the freeway, and then taking the exit and stopping at a light, Idle drops to 600 or 700, and starts to miss, and goes slower and slower until it stalls (note though, the miss is less prominent, and the idle can go even lower before stalling, now that the fouled plug is replaced).

If put in NEUTRAL, idle will pop up as much as several hundred RPM.

If (while in neutral) the engine is revved to 2500 for about 20 or 30 seconds, then idle in neutral will be between 900 and 1100. When put in gear, idle will drop to around 700.

This indicates to me that things are generally still running to rich. I believe the Lambda circuit must be fixed FIRST before I'll be able to correct this issue.


  • The major misfire (once every two revolutions) is now cured.
  • Acceleration is much smoother, and without the "puff puff puff"
  • The constant idle stall when hot is nearly gone
  • The OVERHEATING issue seems to be completely gone. Dash temperature gauge is stopping right on 80C, whereas before it was constantly going above to well above this mark.


  • Idle is still rougher that it should be
  • Idle speed changes drastically when in gear (by as much as 300 RPM)
  • Lambda mixture does NOT seem to be going to closed loop mode, and this more troubleshooting here is in order.
  • I noticed more than usual blow-by today with the air filter housing off (as in some visible smoke) this was most noted when the mixture was WAY off, and I rate it to that, or the fact that I am currently running AutoRX and 10W40, instead of 20W50.
  • There may still be missing to fix, either due to vacuum leaks or plug wires, or something else to be discovered.
  • New Belts squeal at 4000 RPM.
  • Possible loose connection for dashboard temp gauge may be causing misreads (showing too low).


At this point, the next most critical step is to get the Lambda system working correctly in closed loop mode when it should be in closed loop. Until I get THAT working correctly, I am going to be chasing my tail trying to get mixture and idle correct.

While diagnosing idle (after Lambda is truly fixed) I'll be looking closely at the Aux Air Valve, and also the various components in the vacuum system.

After I get Lambda working correctly, and the idle and mixture working correctly then I will replace the other 7 injectors with the new ones & the new seals.

*** My hope is that this is all that is needed to pass smog. ***

Other future replacements (next round of repairs, early next year - will be done before end of this month though if needed for passing smog):

Cap/Rotor/Wires/Plugs (maybe coil??)

Fuel Filter

In 1000 miles, oil filter ONLY change (not oil) per the current step I'm on in the Auto-RX sludge removal program.

Power Steering drain and fill, with new filter (currently running autoRX in it as well).

Transmission drain, filter and fill with Dexron III.

Cooling system drain, flush with DAWN, flush with CITRIC ACID, fill with Zerex G-05.

Check and clean cam oilers. Replace leaking cam cover gaskets.

Steam clean engine compartment.

"Big Future Jobs"

Complete Exhaust from manifold to tailpipe.

Intake manifold gaskets and seals (is it needed??).

Transmission mounts.

Engine MAIN SEALS. Rear crank seal is leaking a LOT. Do this when replacing tranny mounts.

1980 450SL named Freya. 202,000mi
574 Posts
Discussion Starter · #7 ·
Reading with interest!
Thank you :smile

No work on the car today, but I just want to post to note that the reason I am taking things slowly and only replacing a very few parts at a time, is that I want to definitively trace down and determine the cause of each issue.

If I were to wholesale replace all the injectors for instance, and also replace all the plug wires etc etc, I will most certainly make the car "better" but may not actually find all the problems. Making the car better would only make it harder to find each and every problem.

Thus, right now I'm down to the Lambda system as the key problem to be solved. I will not be replacing the plug wires/cap/rotor and the other injectors for instance until the Lambda system is corrected.

1980 450SL named Freya. 202,000mi
574 Posts
Discussion Starter · #9 ·
REPAIR PART THREE (ECU mixture adjustment)


The only repair completed over the last few days was the mixture adjustment. But that was a bigger task than I thought it would be. SO much so it spawned a couple other threads. Over the years, I have attempted to get my car's mixture set properly. Of course, with the problems above like the leaking injector, getting the mixture right was impossible.

It IS possible now that the injector, fouled plug, WUR, and O2 sensor have been replaced.

But - and this is important - it is NOT possibly by using much of the information out there on the web relating to Jettronic/Lambda mixture adjustment - and using the wrong information will be an exercise in futility and frustration !!!!!

It was such a big project (not to mention revelation) that it actually spawned three other threads:

Inside the ECU - a look into the electronics of the K-Jetronic with Lambda system.

Overview and Adjustment of the K-Jetronic with Lambda system.

Suffice it to say, I adjusted the mixture to within an inch of its life. And Freya is running SO nice and smooth now - the loping idle is gone. The stumble is gone.

INTERESTINGLY: She WILL overheat again (I believe due to lean-ness), but not terribly so.

And now that she's running perfect... she's... NOT running perfect.


So now that mixture is correct, I find a fast idle problem. With the idle screw fully clockwise, I can't get idle down below 800 in gear, 900 in park.

Specs (and smog) says it should be 650 +- 50.

Here's an interesting tidbit: When she overheats, idle drops DOWN to 550 to 600.


Based on research I have found that the most likely cause of too-fast idle is most often the Aux Air Valve (or an air leak). The Aux Air Valve is a heat-operated valve that allows in more air during warm-up for the purpose of keeping a higher idle until at operating temperature. But these valves are known to fail, either sticking and naming, or closing at the wrong (too hot) temperature.

Well, it just so happens that when the car over heats, Idle DROPS. This indicates to me that the Aux Air Valve is closing at TOO HIGH a temperature. One possible fix is to remove it, and "slightly crimp" the heat sensitive bulb - the crimp causes it to close at a lower temperature. Our goal is to get it to close at 66C (150 F).


In troubleshooting and adjusting mixture, it appears that the IDLE switch on the throttle is NOT commanding the ECU into idle mode. However, the FULL THROTTLE switch is working just fine. As such, I need to see why the idle switch is not contacting.


In case you're keeping score, that means I am two items away from completion:

1) Idle switch

2) Aux Air Valve

3) Well, there is the third thing of installing the other 7 injectors and seals that I bought, but haven't installed yet.

It's looking like this thread will be coming to a close sooner that I anticipated!!!




1980 450SL named Freya. 202,000mi
574 Posts
Discussion Starter · #10 ·

And Continued Diagnostics

Oct 28, 2014

So I am behind on updating my posts here - but I do have my notes and pictures from these repairs that I will use here.

As noted in the last post, I though I only needed to do the Aux Air Valve, check the throttle switch, and finish the injector replacement. Well, I was wrong, but more on that as I continue the diagnostics.


The Aux Air Valve is part of the Idle Air circuit. When the engine is cold, the AAV is open, allowing substantially more air into the idle circuit to increase cold idle. When the engine heats up, the valve is supposed to close off completely, so that only the air idle adjust screw sets the idle speed.

As you may recall one of the car's symptoms was that as it overheated, idle dropped so low the car would stall. I had originally though the problem was somehow related to the WUR and its broken heating element, but I believe that diagnosis is not really correct. The WUR did need to be replaced due at least to the broken heating element - but the WUR was not related to the low idle when the car overheated. The AAV is responsible for that symptom.

The reason for the symptom is that the AAV was not fully closing till much hotter than its spec - it was closing around 95C. It SHOULD close at 66C. Because it was not closed at normal operating temperature, the IDLE SET SCREW was adjusted too low in order to get the "correct" speed at normal temp. Then as the car overheated and the AAV closed further, the idle became too low (500) and the car would tend to stall.

The AAV is a very expensive part ($830 at some outlets), and yet it is very simple. A bulb at the base filled with oil that sits in the engine coolant stream, and pressed a plunger as it heats up to close a spring loaded valve. I was not about to spend $830, but fortunately, there is a way to adjust the AAV closing temperature, which I will discuss later in this post.

First, I needed to remove the AAV. And about 1 AM I was attempting to remove the auxiliary air valve and one of the bolt heads broke off. UGH!


I ended up waiting until the morning and driving out to "Your Dream Garage" so I could have a better place to actually work on removing the air valve, dealing with the broken bolt, and cleaning and adjusting the closing temperature of the valve. I ended up spending about five hours on the single task simply due to a number of complications in the process.

Your Dream Garage is a wonderful DIY garage in Baldwin Park (Los Angeles) where you can rent a lift and all the tools you need for 25 an hour, or stall space with tools and no lift for 15/hr. I've been doing all my serious work there as it's way more convenient to use a real parts washer and nearly all the tools one would need (No Mercedes specialty tools, but nearly everything else).

I ended up buying the pre-paid "VIP" package which gives me a discount on the total cost per hour, and includes free drinks (Gatorade, Pepsi, etc), and set out to work on the AAV. The second bolt came out easily, and a tap from a rubber mallet got the AAV free.

The Dream Garage has a real parts washer, and I used that to fully clean out the AAV. I tested the closing point by putting it in water about 150 to 160° as determined by an infrared thermometer.

It wasn't closing so I got it hot in the water to about 160 F, and put the bulb in a vice attempting to make it close at a lower temperature (target temp is 150 F or 66C). I attempted to be methodical, and only close it a little at a time, then test and repeat - but what I *thought* was the visible closing point was actually well past the closing.


What I SHOULD have done was shine a light through the valve while it was in the vice, to *really* see the closing point. In short, I squeezed it a bit too far, and now it is closing early. Not "terrible" as I live in warm climate California, but I'd say the first two minutes of operation from a morning cold start are a little off in terms of the idle is now too slow before warm up.


I plugged the AAV hole with a rag to prevent debris from falling to the manifold, and scraped the old gasket material and cleaned the area.

In order to remove the broken bolt I put a lot of penetrating oil on it and scrubbed the area with a wire brush, waiting about 30 minutes between applications - but it still wouldn't budge after three applications so I took a steel punch and hit it twice (dead center) with a ball peen hammer, then clamped the stud with vice-grips and applied torque until eventually it "clicked" and I was able to free the broken bolt . I took a thread die of the same size to chase the threads then I replaced the auxiliary air valve that I had adjusted and cleaned, using a new gasket.

Unfortunately I had not purchased yet the replacement black hoses that go to the auxiliary air valve which was a huge error on my part as the black hose that goes to the manifold into the idle screw broke during removal because it was so vulcanized hard.

In order to get the auxiliary air valve back on I further had to saw the rubber hose put the pieces on and then epoxy see them and use permatex 2A gasket sealant.

(Note permatex 2A may be a bad choice as it may not be oxygen sensor safe and it may have contributed to the oxygen sensor problem, to be discussed next post.)

I'll be replacing the hose as soon as I receive from AutohausAZ this week. TIP: Have THIS hose on hand BEFORE removing the AAV.


I have reason the believe the AAV and the O2 sensor were the PRIMARY causes of the "run bad" problems I've been having, and the WUR and Injectors were secondary issues. I'll be discussing this in the next two posts. But in general the symptom:

"Idle drops when car overheats, with idle set correctly at normal operating temp"

Is pointing the finger at the AAV closing temp.


380SL diesel
1,275 Posts
Great read - I love your methodical approach and perseverance, and diagnostic and troubleshooting skills. Great job. Of course it made me ever more thankful that I replaced the gas engine in my 107 with a diesel so I don't have to worry about CA smog at all ever again....or plugs, cats, EGR, WUR, AAV, ECU, lambda and so forth.

1986 560 SEC 1987 560 SL 1967 250 S (sold)
1,385 Posts
Wow Myndex, you and me are fighting a similar battle! Wish I could help but you have been helping me. I wonder if your intake is leaky??

thanks for your detailed postings,


1980 450SL named Freya. 202,000mi
574 Posts
Discussion Starter · #13 ·
Great read - I love your methodical approach and perseverance, and diagnostic and troubleshooting skills. Great job. Of course it made me ever more thankful that I replaced the gas engine in my 107 with a diesel so I don't have to worry about CA smog at all ever again....or plugs, cats, EGR, WUR, AAV, ECU, lambda and so forth.
Thank you. I *had* hoped that by now my car would not be requiring smog - when I bought it in 2000, CA still had a rolling exemption. I'm a little sad that they froze that at 1975.

Wow Myndex, you and me are fighting a similar battle! Wish I could help but you have been helping me. I wonder if your intake is leaky??
Yes, I was noting some similarities to what you are experiencing. I did test intake leaks (to be discussed in a later post) but may be looking there again soon.

1980 450SL named Freya. 202,000mi
574 Posts
Discussion Starter · #14 · (Edited)
REPAIR PART FIVE and continued diagnostics Oct 29, 2014

After taking care of the AAV, I spent some time trying to set mixture - I did after all have a new O2 sensor in there. But alas, it was starting to act "odd" after only a couple weeks of service.

What was the problem? At idle the Lambda system would go to full enrichen, as if the O2 sensor were detecting a very lean exhaust. But worse, when the O2 sensor was not up to temperature yet, the lambda system SHOULD be locked at 50% constant. And it wasn't - with the O2 sensor not at operating temp, the lambda system would drift down to 95% duty cycle.

According to the Mercedes service manual, this indicates a short in the sensor. According to some sources, it could mean the sensor is contaminated, or "poisoned" such as by silicon or coolant.

The old O2 sensor (installed years ago) was in fact partially coated with a whitish powder, evidence of coolant contamination. Had the new sensor already been killed by coolant in the exhaust stream?

I am aware that there must be some coolant leaking issues in my car, while they aren't severe, they do occur, and I'm not certain if they are in the intake manifold, or the head. As I have good compression, I am making the assumption that it is NOT a head gasket issue, but one cylinder is in fact weak enough (cyl 5 is 7% lower than others) that I have to consider that there could be a small coolant leak in the head gasket.

As my primary goal right now is to pass smog, I am looking first to dealing with those direct issues. Not knowing why my new O2 sensor is not working correctly, I bought another one just in case. The new one was a DENSO, which is touted as being more resistant to poisoning. It has an extra "cage" around the sensor that is supposed to make it more resistant to silicon contamination.

I bought the Denso for $17, and since I was going to be under car for this, I picked up a fuel filter as well.


Just some quick notes on fuel filter replacement.

1) Make sure when you buy the filter that it comes with two copper crush washers. The parts place tried to sell me a filter that was missing the washers, and they are needed for a proper pressure fit.

2) wait till the tank is nearly empty, and you won't need to clamp the fuel hose.

3) Even so, remember that the fule filter itself holds a pint of fuel - make sure you have a drip pan to catch it as you disconnect the fuel fittings.

4) When I loosened the connecting hoses to the fuel filter and the fuel came pouring out, I really wish I had been wearing a nosh 99 respirator mask because spending that time with all that fuel & fumes gave me a bit of a headache. Even just a pint of fuel is nasty to be sure.

5) After installing the new filter and it is secured in place, use a sharpie to write the date and mileage it was installed on the filter housing.


This is the main point of this day's repair - finding out what is up with the sensor. First off, I spent some time checking the continuity and resistance of the electrical connections for the O2 sensor.

WARNING: Do not use an ohm meter on the O2 circuits while the O2 sensor is connected, as you can damage he sensor.

I disconnected the O2 sensor and unscrewed it from the exhaust pipe. I examined the connection where I had crimped to the existing connector. it appears that there was one tiny filament of wire from the connector's braided shield that may have been intermittently contacting the oxygen sensor's main conductor. As a result it was intermittently shorting out to ground, setting the lambda system to full enrichen.

This explains the erratic behavior. And while the short probably did not damage the O2 sensor, as I had already purchased yet another one, this time a Denso instead of the Bosch, I opted to use the new Denso sensor and install it, taking greater care this time on installation.

Also on examining the bulb of the oxygen sensor, It was quite covered in carbon showing that the car is still running rich. Examining the oxygen sensor wires and the wiring harness for the car I saw that there was some exposed wire on the chassis side of the connector however that exposed wire at the strain relief of the connector appears to be only the shield (nevertheless, I would repair)..

As the oxygen sensor connector lead was getting shorter every time it got clipped, instead of clipping off the oxygen sensor I took Vice grips and forced the crimp 90° from where it was originally crimped, releasing the wire without cutting so I wouldn't lose more wire from the connector.


With the old oxygen sensor removed from the connector, I connected the connector by itself to the chassis connector. I disconnected the ECU from the chassis ECU connector and then using an ohmmeter I probed the resistance between the oxygen sensor connectors and the ECU connector.

The overall circuit resistance for both the center conductor and for the shield ground was approximately 0.6 ohms. There was no indication of any kind of a short and I spent some time exercising the wires and wiggling them to see if it was possible to induce an intermittent short but the wires seem fine.

In checking the ground path from the exhaust pipe to the chassis ground I found the resistance to be more like 1.5 k ohms to as much as 4.5 k ohms depending on the points selected. This could potentially result in an incorrect signal to the ECU, depending on the impedance to the input of the ECU. I am considering that it might be appropriate to provide a direct ground to the oxygen sensor and the chassis using a braided grounding strap. (Note: I do this in a later repair session, details here).

Installing the new sensor:

I took extra care dressing the wire from the connector - I stripped the shield portion back farther a couple millimeters and made very certain that all of the strands of the braided shield were fully trimmed back.

The oxygen sensor lead was trimmed to the appropriate length and stripped.

I slid the heat shrink tubing on and then used the wire crimper (vice grips) to crimp the connector and oxygen sensor together. Unfortunately this supplied heat shrink tubing wasn't long enough to cover both the crimp and the area where I had trimmed the shield back so I favored the wires at the crimp and I used electricians tape and a ziptie to add insulation on the connector side.

(unfortunately I had left my supply of heat shrink tubing at home but in a pinch electrical tape works - it's just important to use a cable tie to hold the electricians tape in place as it certainly won't stay there on its own.)

Denso provided a generous quantity of anti-seize compound - this looked a bit different from that supplied by Bosch as the Denso material appeared to be very high in copper content which should help it's conductivity through the connection to the exhaust.

Nevertheless, I am still considering adding a grounding strap to secure the ground for the oxygen sensor as I consider it may improve performance due to the age of the exhaust system. A direct ground should help to reduce noise in the oxygen sensor circuit which may be causing interference problems with the ECU. (And I did in a later repair session)

I covered the threads with the compound, being careful not to get any near the sensor shield.

I threaded the oxygen sensor by hand into the exhaust pipe and twisted it back-and-forth A couple times to make sure that the anti-seize compound was thoroughly spread through the threads and then torqued the oxygen sensor with about 40 foot pounds.

I covered the bare shield on the chassis connector with electrical tape, and secured that with a zip-tie, which should help keep the shield conductor corrosion free and keep fluids out of the connector housing.

The oxygen sensor's chassis electrical connector has a little box for it to sit in just above it's location at the exhaust pipe. If you look at the holder it appears that the end may have had a place to use a clip - as I don't have a clip I used a zip tie to make sure that the connector was held securely in place so that it wouldn't vibrate. I failed to do this last time and I consider that vibration may have been a contributing cause to the problems with the previous oxygen sensor.

Adjustment and evaluation:

I started the car up there was some initial hesitation because the new fuel filter was of course empty - I used a trick where I put the car in gear and then turn the ignition all the way to start for five seconds. This runs the fuel pump and fills the filter with fuel.

Then the car easily started and It was immediately apparent that it was running better already.

Looking at the oscilloscope I can see that this oxygen sensor was not shorted, so the duty cycle trace was right at 50-50 constant, which is where it should be with the oxygen sensor not at operating temperature.

(Note if the oxygen sensor is not an operating temperature but the lambda system indicates a full rich duty cycle that indicates that the oxygen sensor is shorted out.)

Image from the thread "Adjusting K-Jet With Lambda".

After the oxygen sensor was at operating temperature and I saw the "heartbeat pulse" of the sensor working (ie, the duty cycle was fluctuating already 15% range) I made some minor adjustments to the mixture screw on the fuel distributor to get the duty cycle where it needs to be, which is pulsing between 40 and 60%.

With the mixture apparently correct the car was running much, much better than it has in quite some time. Once the car had reached operating temperature, I adjusted the Idle to 650 and the car's idle seemed both stable and smooth (at least compared to what it was!).

With the new oxygen sensor and fuel filter, the car was running remarkably well with excellent acceleration and very smooth Idle when warm. Idle is still a bit rough when the engine is cold for the first one or two minutes after starting the cold engine (possibly due to over-correcting the AAV valve temperature as noted in the previous posting).

Further diagnostics:

The new oxygen sensor is much more sensitive to mixture changes at Idle with the engine not under load which means that conditioning during rough adjustment can be done without actually having to drive (as I had indicated in the thread on lambda adjustment.) I believe this is because the previous oxygen sensor had the intermittent short problem.

However I can't escape the possibility that there may be coolant fouling the oxygen sensor, so I am planning on getting the car smoked as soon as possible while this oxygen sensor is operating correctly. If there is a coolant leak my first assumption is that it's in the intake manifold gasket because my compression test a couple weeks ago indicated that all the cylinders were pretty strong with compression.

After driving approximately 100 miles today, mostly on the freeway driving, I found the oxygen sensor would attempt to enrichen all the way to the enrichment stop at idle, indicating that there is possibly some form of an air leak causing an overly lean condition when idling.

Even so the engine idle is still very smooth, And freeway driving is excellent. I'm estimating my fuel consumption is back down to 15 miles per gallon and it hasn't been that good in years.

My last check today was the throttle switch - and I confirmed that the switch commanded at IDLE STOP and THROTTLE FULL.


As it happens, I completed this work (at Your Dream Garage in Baldwin Hills), at mileage 199,995. So Freya and I had a fun fast drive home, her purring like a kitten finally, and we celebrated her 200,000 mile rollover/birthday on the way. Tomorrow (Oct 30) I am going to replace all the injectors to be ready for my smog test on Friday Oct 31.



1980 450SL named Freya. 202,000mi
574 Posts
Discussion Starter · #15 · (Edited)

Early on I felt that the cylinder #1 injector was leaking and replaced it (and its fouled plug) and that seemed to cure a lot of problems. But when I bought that injector, I bought a full set. As I am now planning on getting the smog check tomorrow, I decided to replace the other 7 injectors, as well as check my installation of the first injector.

In preparation for installation, I coated each of the black rubber seals and the injector barrel, in a light coat of trans fluid (my preferred medium oil for light assembly - I think WD40 is too light.) This helped to get the seals properly placed on the injectors as they are a very tight fit.

It is useful to note that the only thing holding the injector IN are these black seals. They fit tightly to the notch on the injector body, and when compressed in place hold the injector in its seat. If these seals weren't there you could literally just pull the injector out.

I cut the ends off some popsicle sticks, which I used to help clean the nooks and crannies in and around the injector ports.

In prepping the injectors I kept the plastic protection cap on to keep the inlet clean during assembly. I also applied oil to the O-rings of the plastic seats.

Prior to removing the old injectors, I used brake cleaner to spray away the bulk of the dirt and grime around the ports - but there was a lot (and even more inside).

For removal, use a 12mm box end on the injector body for counter force, and a 14mm box end on the fuel fitting. Gas will come out of the first one under whatever residual pressure is in the system, so have a rag to catch that.

You may want to disconnect the plastic fuel line clips to allow the fuel lines some freedom of movement. After the fuel line is disconnected, remove the bolt to the hold down plate, and then you can just pull out the injector. Note that on the drivers side, to remove the #8 injector, you will have to also remove most of the fuel system connections on that side, just so you can get to the hex bolt on the regulator shaft. Seriously, if the shaft were ½" inward it wouldn't be a big deal. But it's not, and you have to remove the fuel pressure damper, frequency valve and several fuel lines just to get to it. Grrrr!

The injector's plastic seat is a bit harder to remove, as it will likely be jammed in there pretty good with decades of grease and grit. I found using a pair of vice grips and rotating while lifting worked best. While I'm discarding these old plastic seats, I don't want them to break and have pieces fall into the intake manifold and be eaten by the engine - so work slowly.

Here's the old vs new injectors and seats. Note the old plastic seat is missing its O ring (hint: Its still in the port!!)

As you can see, these ports are totally gunked up, and I DON'T want to spray-clean the stuff into the intake manifold!! To get the loose debris, I wrapped the squared-off end of a popsicle stick in a piece of shop towel, and dipped it in oil, to help it pick up the loose grime and grit. Then I carefully wiped the interior of the port with a clean, lightly oiled rag wiping upwards and discarding each wipe.

Here is a partially cleaned port. The tip of the plastic seat fits in the smaller hole, and the Oring seals to the larger bowl shaped port. You want to get all that crud out without having it fall into the engine.

Importantly, you'll find that most of the old cracked and hardened Orings will still be in these ports after you remove the plastic seats. Be careful when you take out the old brittle Orings as many will break and may fall into the engine. (I lost about 1/3rd of one to cylinder 7 - UGH!). In short, if you don't see the O ring on the old plastic seat when you remove it, look in the bore, because it'll be there!

A 19MM socket fits nicely into the top of the plastic seat. I used this with an extension and a rubber mallet to work the seats into the ports.

First, lubricate the port and the plastic seat and Oring with oil, then using a twisting motion work it into the port so that it is even and the O ring is not binding on the outer edge. The using a rubber mallet and the socket, gently tap the plastic seat into place.

Next, clean the metal hold-down plate, and put it on the new injector. Replace the injector's protective cap which will both hold the hold-down plate in place as well as protect the injector from dirt until the fuel line is attached.

Then just slide the injector into its plastic seat (The plastic seat insulates the injector from heat to prevent premature fuel vaporization). Clean the hold-down bolt and give it a little WD40 to light oil, and thread it in by hand for a few turns before using the ratchet. Torque down to wrist tight (You'll see the injector seal deform under the pressure).

Here are the left bank of injectors, ready to be re attached to the fuel lines.


I didn't really notice a huge difference in performance, but then most of the problems I have been fixing were related to more serious component failures. I had hopes that replacing all the injector seals and O rings might help smooth out the idle, but it really had no effect. Still, the car is running MUCH better overall with everything done this week. I tweaked the mixture just a bit using the oscilloscope, and TOMORROW it is SMOG TEST TIME.


1980 450SL named Freya. 202,000mi
574 Posts
Discussion Starter · #16 · (Edited)

Oct 31, 2014 (last day before my tags expire).

Before bringing the car back to the smog guy, I took it out for an extended freeway run, to get it fully heat soaked. The tank had premium in it.

On arriving at the smog guy's I told him the substantial work I had done, and that I felt it was time to try a retest.

He looked over the car, but he felt that it was still misfiring at idle (there is a slight putt putt gong on).

He put the car on the dyno, and

---- FAIL. ----

---- FAIL. ----

CO was 2.0%. HC was a hundred something, but in limits, and NOx was about 1200 - just barely in limits. Limit for CO for this car is 1.25%.

The smog guy felt that the misfire is what resulted in the fail. The thing is, I'd think a misfire would have given much higher HC readings.

So, tail between my legs, I bought the california extension, ($50) which gives me till Dec 8th to bring the car into compliance.


The story continues:

It's far from over. The key factors now are the slight idle problem (putt putt putt), and the "rich smell". Obviously the car is running too rich with a CO of 2.0. This and the misfire (probably interrelated) will be the subject of the ongoing diagnostics.

At this point (Oct 31), considerations I have are:

1) O2 sensor is not well grounded, just being in the old exhaust pipe.

2) I have not replaced the spark WIRES, CAP and ROTOR (all about 65K old).

3) There may be air leaks I have not yet found.

4) And another possible issue is the ticking heard in the right bank - a weak hydraulic compensator may be causing a "breathing" problem that results in a misfire.

5) Could the fuel distributor be at fault? I hope not.

Till next post..... :banghead:


1980 450SL named Freya. 202,000mi
574 Posts
Discussion Starter · #17 · (Edited)
Nov. 02

Well, it's pretty disheartening after doing several weeks of work, and getting the car running better than it has in ten years, to STILL fail smog. While the smog guy pointed to the missing, the High CO seemed to me that it was more a "too rich" situation.

What could cause it, with a brand new O2 sensor installed?

Well, as I noted previously, the O2 sensor being installed into the 34 year old exhaust was seeing about 1100 ohms resistance to ground. While I don't have a schematic of the ECU, and as trying to examine the input stage would be destructive, I don't really know how much such a resistance would throw off the O2 output and therefore the ECU. But my feeling is that what appears to be a mostly passive input stage in the ECU probably does not have a high enough impedance that an 1100 ohm resistor placed where it shouldn't be would not have an impact.

So, I decided that I should improve the grounding of the sensor by adding a grounding strap, as I detailed in this post.

How to re-ground your O2 sensor for better and more accurate response.

With that out of the way, I hoped to get a more accurate mixture. I was also getting tired of lugging my oscilloscope around in the front seat for diagnosing the mixture and lambda/O2 sensor operation, so after some research I came up with this simple modification that allows you to use a standard duty cycle meter to view the duty cycle of the lambda system.

ECU modified to allow a standard duty cycle meter to measure the duty cycle of the lambda system.


Now, I had not planned on replacing the wires, cap and rotor, but at this point I needed to make sure the car was "as fit as possible". The wires cap and rotor had about 65K miles on them (maybe as much as 75K), and while I felt they were fine (I did test the resistances) there was some heat damage to some of the wires. I ordered the Bosch cap and rotor from AutohausAZ ($37 for cap and $12 for rotor). I ordered a set of Kingsborne wires ($98), and I also ordered the heat protective sleeves ($28).

To be complete about it, I also ordered from AutohausAZ the little plastic connectors for the cam oiler tube as these were also last replaced about 70K miles ago when I had the timing chain done. I already had the valve cover gaskets on hand (I have been wanting to fix the cover leak for some time), but what I didn't have on hand were the copper crush washers for the valve cover bolts, so I ordered 16 of them as autohausAZ indicated that 8 were needed per cover - this is wrong, there are only 4 per cover and 8 total per car.

Part of my interest in pulling the valve covers was the light tap I was hearing, not sure if it was related to the misfire but I did want to investigate.

I also bought a new air filter - as I looked at my old one, it was kinda dirty.

While I waited for the parts to arrive, I did a lot of freeway driving every day - test drives, my favorite part!


First off I swap out the air filter. This time I wrote the date and mileage on the rubber part with a sharpie, so in the future I'll know for certain how old it is.

Next, I prepped the cap and wires. Using some dielectric grease on the cap contacts and inside the rubber boot of the diet. end of the wires, I pre-set all the wires on the cap so when I brought it to the car, it would be a super easy swap out.

The black knit looking tubes are the high heat shields, which are good to 1200 degrees F - high enough they can sit right on the exhaust. my last set of wires were heat damaged by the exhaust manifold, and I didn't want this to happen again! These slip on the plug ends - with the Bremi metal connectors, they snag just a bit, but treat them like a Chinese finger puzzle and push the two ends towards each other to temproarily increase the size of the knit tube, and they'll slide on easily.

I bought all black, but later I wish I had bought two of each color - then I could have color coded the wires for each cylinder. Interestingly Kingsborne numbers the distributor ends, but not the plug ends.

Because the wires are all additionally protected by a (silicon?) sleeve, it is necessary to identify each wire before assembly (just pull on each one to identify). I then marked each plug connector with a sharpie to ident the correct number.


I went to Your Dream Garage to pull off the valve covers. I did the right bank first as this is the one with the cylinder that was missing, and also the bank with the noise.

Here's a video of the cam turning with the engine at idle:

Remember its cylinder ONE that has the missing issues, but it sounds like its cylinder THREE (or FOUR) that is making the biggest TAP sound.

Also note that while I'm happily taking video of this, the oil is dripping down more that I realized. LOL. Years ago when I was having the timing chain replaced, the mechanic ran the car at idle to show me how the cam oilers were not getting oil to the forward cam lobes. He obviously had a large oil pan under my car. Me on the other hand - I didn't realize I'd lose a few quarts running the car with the cover off for under a minute.

I ended up with a big oil spill under the car to clean up. Fortunately, CHANCE, the owner of Dream Garage is a great guy and helped me clean it up, not charging me for the several absorbent oil pads we used in doing so. It's not a mistake I expect to ever make again. UGH!

But, at least we have the video!

After shutting the engine off, I checked for play in each of the rockers with the cam lobes pointed up. No play anywhere. I then used a wood hammer handle and I could not depress any of the lifters.

I did NOT have a go/nogo gauge, and I suspect that is the next step. I also did not have a spring compressor, so I couldn't remove the rockers to examine (yet). I suspect that perhaps I need to replace one of the shims. I should add that years ago at the timing chain change, the mechanic also replaced the glided oilers, AND a few of the rockers that were extra worn due to oil starvation. I don't believe he checked or replaced any shims though, and I supposed that may be the cause of the ticking.

On the LEFT bank, cylinder FIVE (which if you recall is the weakest cylinder in the compression test) is the one with the most severe cam lobe wear. However, the wear you see is essentially what was there 70K ago when the mechanic renewed the oilers and replaced the two rockers there. It is useful to note that all the cam lobes on the other cylinders are pretty smooth in terms of roundness. These two lobes are the only two with any kind of ridge you can feel, on the trailing edge of the lobe. it's so slight though you can't see it, just feel it.

Nevertheless, Cylinder five is NOT the cylinder that is misfiring. The plugs in 5 look just fine. It is ONE that is the main misfire culprit. And the cam lobes seem fine and the rockers are quiet.

Finishing the job, I cleaned out the valve covers in the parts washer, getting all the nasty gunk out of them and the PCV chambers. I removed the old plastic bits from the oiler tube and thoroughly cleaned it as well.

WARNING: Do NOT use pliers to remove the old plastic bits! the oiler tube is very soft aluminum, and if you slip you'll scratch the crap out of the tube! (Yea, I did... sanded it with 600 grit wet).

Lightly oiled the tube with fresh oil, and slid the new plastic bits on, making certain to align the holes with the holes in the plastic holders. Setting it back on the cam towers, I noticed it was a bit warped, so I very gently straightened it out. I secured it in place by using a small block of wood and a rubber mallet, going up and down to each point several times knocking them into place.

Then. I lightly oiled the new cover gaskets, which slip on over the edge of the valve cover. My old gaskets were pretty hard in some places and leaked badly - I hoped to cure that, and so I tried to be "by the book" as much as possible. I cleaned the old head outside edge thoroughly using a clean rag and some brake cleaner. I also cleaned the old bolts, and gave them a squirt of WD-40.

Next, I slid acopper crush washer on each of the bolts, then the bolts into the cover.

It's a bit more tricky getting the cover back on than it was taking it off, but the right bank covers isn't so bad. Unfortunately the LEFT bank cover requires disconnecting some rules lines and the brake vacuum connection to R&R the left cover. The main thing in setting it in is to make certain the cover does not come out of the groove of the gasket.

The factory spec for torque on these bolts is TINY - 3 Nm, which is 2.2 ft/lbs or 26.5 in/lbs. Fortunately Dream Garage has a small torque wrench just for that. After finger tightening the bolts in, I torqued them to 3 Nm. This seems about "as tight" as you might do with a hand held screwdriver, but not a ratchet. I have reason to believe the last mechanic to tighten these covers way over did it, as the old crush washers were really thin, LOL.


After cleaning the excess oil spatter, and removed the old cap, rotor and wires. I found the dust cover for the pulse sender should be replaced, but I don't have one on hand, nor do I see it in any of the parts suppliers. ??

Nevertheless, I installed the new rotor and cap, and routed the wires to their plugs. I smeared some dielectric grease on the plugs and inside the Bremi connectors. THE GREASE IS IMPORTANT. these connectors are very tight, and you need the grease to allow you to get enough force to get the connector on all the way. You need to hear it "ratchet" on the threaded plug connector.

(Oh yes, these wires are OE style, and require a threaded end on the plug.)

With the plugs in and everything buttoned up, I started her up. The misfire is STILL present. However, as it could be due to a fouled plug, so I am going to drive a hundred miles on the freeway and do a Sea Foam application to see if that helps.

If not, I'll swap plugs out and take it from there. (I should note that the plugs that are IN are WR9DC+, that were installed just about 2000 miles ago by the indy in July).


1980 450SL named Freya. 202,000mi
574 Posts
Discussion Starter · #18 · (Edited)
Part EIGHT - Mainly diagnostics.

As the wires did not cure the misfire, I replaced the plugs with NGK Iridiums. While consensus is never to use Platnums in these older cars, there is mixed feelings on iridiums. I decided to go with them as they are more resistant to fouling. Nevertheless, replacing them did not solve the misfire.

Okay, so the recap thus far, we have brand new injectors, wires, plugs, and the related components. Why are we misfiring?

I decide to dig deeper.

There was a closeout on Bexk/Arney Valve seals at RockAuto, so I bought a couple sets. Also, as I was unable to examine the rocker arms under the valve cover last time do to the lack of a spring compressor, I bought this one for $62 from KTC tools on Ebay:

Not badly built, though they have the handle backwards, and in removing the snap ring, the snap ring broke, LOL. Stiil, a solid hunk of metal.

With that I headed off the YOUR DREAM GARAGE, the DIY auto garage I use for "more complicated" work.

First off, let's take a look at the misfiring cylinder 1's plug. About a hundred or so miles on it, and yep, it's carbon black. Interestingly, this iridium plug does indeed have a cleaner tip despite the carbon fouling.

On the the main reason I'm here - to inspect the valve hardware for cylinder one, and possibly replace some valve stem seals.

I used the new KTC tool to compress the springs, but I found the alignment of the tool handle is essentially backwards - but in removing the pivot pin, I broke the snap ring that held it in place. Ultimately, I found that using their tool required a bit of adjustment and finesse - the hooks for instance are a tad long for easy insertion under the cam. I may modify the tool in the future,

Looking at the rockers, they seemed fine, normal wear.

With the rockers out, I figured I might as well remove the hydraulic compensations (they aren't really lifters, but are typically referred to as such). I removed the sludge under the lifters, and cleaned their oil galleys with a thin brush. The lifters seemed in good condition and solid. After cleaning I re-torqued them in at 60 Nm.

You can see the white nylon rope I am feeding into the plug hole - after feeding in a few feet of rope I rotated the crankshaft to put a firm hold under the valves prior to removing the springs.

Getting the valve keepers out was more challenging than I thought. Typically I could get the top half, but the bottom half proved more difficult. I suppose the "real" mercedes valve keeper tool would be useful, LOL. Instead, here is the work-around:

Use a very strong magnet (the red one here), and attach it near the tip of a flat blade screwdriver, then use the screwdriver tip to extract the valve keeper. The strong magnet's force is directed through the screwdriver tip, making the screwdriver a strong enough magnet to extract the keeper.

I then removed the springs and related hardware. I find it interesting that MB uses two springs (one thick and one thin), I am also fascinated that at the base is a bearing race that allow the spring to rotate. Wow, some pretty cool engineering here.

The old valve seals didn't look too bad, but I removed them anyway as I wanted to feel the play in the valve guides. There is a slight amount of play in the intake valve, and less in the exhaust. Both rotate, with the exhaust valve being a bit more difficult to rotate.

The new seals went on fairly easily, even though I didn't have the mandrel - the intake valve I placed the plastic tube over the valve stem. I coated the new seal in fresh oil, and slid it on. A box end wrench worked great to get the intake seal to click into place (it is a firm snap).

The exhaust seal is a different matter. If you try to press it on using a box end wrench, the seal will just buckle. so here is the workaround:

Take a very small hose clamp, and lightly clamp it around the exhaust seal. This will keep the seal from buckling, and you can press it into place using a box end wrench of the appropriate size.

I reassembled everything, and on reassembly I thought I was feeling some tension in the exhaust valve - this lead to a thread here where I thought I might have had a warped valve.

Consensus here though was that with my good compression readings and the other symptoms a warped valve was not so likely, and in retrospect I have reason to believe that the tension was the valve spring tool rubbing on a fuel line.

As it happens, I only replaced the vale seals for cyl 1. Why? It was taking quite some time, and I pay by the hour - I'm not really burning oil, and the reason I did cal 1 was more to check the quality of the valve movement and play, replacing the valve guides was just a necessary part of that.


After discussion in the "warped valve? help!" thread, the conclusion I found most likely was a bad fuel distributor.

Initially, I dismissed the distributor as I had erroneously thought it had a stainless steel diaphragm and was more likely to fail lean.


The fuel distributor diaphragm in THIS car is rubberized fabric, and when it fails it fails RICH.

To be continued.....


1980 450SL named Freya. 202,000mi
574 Posts
Discussion Starter · #19 · (Edited)


In a way we've come full circle. As you may recall, in my first post I indicated that my diagnosis was a leaking injector causing cylinder 1 to be too rich. Changing the injector and the folded plug seemed to improve things greatly, but not "fully cured". I believe that this is be cause a *weak* injector was allowing more fuel due to the defective fuel distributor, and a *new* injector lessened that a bit.

Still the misfire continued, and everyone I talked to had different thoughts and ideas.

It was FONZI here that pointed out that fuel distributors for THESE cars tend to fail RICH. And further research showed that to be true.

Here are corroborating reasons to suspect the fuel distributor:

1) Problem is worst at idle, and lower RPMs. At 2500 and above, the engine smooths out. This is partly because the "excess" fuel in cylinder catches up to the other cylinders and becomes closer to the "correct" mixture.

2) Idle after extended freeway drives is better - this is because of the above, the plug is able to self clean and be less fouled.

3) Idle after stop and go traffic is worse, this is because that cylinder is operating more at speeds where the rule imbalance is most severe, causing greater fouling of the plug.

4) My gas mileage sucks.

5) After stop and go or extended idle, there is a definite rich fuel smell.

I beam so convinced that it was the fuel distributor I didn't even do further tests. Neither of the main rebuild shops (Flowtech and SpecialTauto) seemed to have a unit ready to go. I happened across a couple different rebuild kits on Ebay, and I went with the APM brand, as is detailed here:

(click here) Analysis and choosing the rebuild parts.

I then performed the rebuild. I did the "minimum" build, not touching any of the adjustment screws, as I don;t have the elaborate test equipment needed for aligning the flow on these.

(click here) The Actual Rebuild and Test.

And the proof? Here is the before and after tail pipe idle of my car.


I have a Mercedes again!!

I still must pass smog, but now, I believe I have a solid change to make smog, no problem.

The things I am going to do next are:

1) Drive a couple hundred miles at freeway speeds to blow the carbon out.

2) Complete oil change, so I see the smog guy with fresh oil.

3) On the day of the smog check, drive at freeway speeds in the morning for at least 40 miles and get the car heat soaked.

4) I am NOT going to pour denatured alcohol into the tank to improve ratings, though I am considering putting in an octane booster (would love to hear thoughts on this).

Other things to do with my car now:

1) Radiator. I found the reason I leak coolant:

2) Trans fluid complete drain with filter change. Debating if I should use Sea Foam transtune before the change.

3) Power steering drain and filter change. I put Auto-RX in there a couple thousand miles ago, time to change it out for fresh fluid.


1) Fix the windshield washer reservoir - I bought sufficient parts at the junk yard, so should be easy.

2) Fix the heater blower motor.

3) Fix the climate amplifier and reconnect the heater core, etc.

4) Remove steering wheel and address the minor issues in the instrument cluster.

5) Replace the passenger door with the one I just bought, and adult the glass for my car (it was an SLC door). This is not just cosmetic, the window regulator on my current door is shot.

6) Take the door stop from my old passenger door, and put it in my driver's side door (which has been broken for ages due to valet drivers shoving my door open all the time).


1) Fix left quarter panel dent, and temp paint the correct color.

2) Temp paint the new SLC door to match (its a lighter blue).

3) Install my new interior panels and parts. Dye certain existing parts to parchment (currently Palimino)

4) Either replace my seats or reupholster them.

5) Patch the knife cut in the ragtop. No, I am not going to buy a new one till I live in an area where it won't get knifed every 6 months. I;m just going to patch it and stow the hardtop.

6) Fix the stereo.


Strip paint and do a very slight color change. I am thinking:

Which I think will look great with the white parchment interior.

Once I pass smog, and this thread is concluded, I'll complete the table of intents and bibliography. I hope the thread has been helpful to anyone diagnosing these tricky cars.


1980 450SL named Freya. 202,000mi
574 Posts
Discussion Starter · #20 · (Edited)
PART TEN - Smog Pre-Check FAIL and further repairs.

Okay, so Saturday (Nov 22), I did a full oil and filter change in preparation for the smog check. Also did a full automatic transmission oil and filter change while I was at it.

Then filled up with Chevron Premium, and did some "spirited" freeway driving over the weekend.

How can a pretty car like this actually fail smog?!!?

On Monday morning, I took Freya out and drove about 25 miles, mostly freeway, stomping on it, and took it to the smog guy Ken (who has been very very patient and helpful).

While I had to wait for a car in front of me, I don;t think it would have mattered - the pre-test was WAY off for NOx.

WAY, like 1800. On the other hand CO was FAR better at 0.95. HC was slightly off at about 210.


Okay, so first off, here are my smog results from Oct. 7 2014 - this is after Ken spent time trying to adjust (at that time a very poorly running car) into compliance:

So the LIMITS for my car are:

TEST ---- MAX HC ---- MAX CO ---- MAX NOx
15MPH ... 191 ........... 1.25 .......... 1277
25MPH ... 159 ........... 1.05 .......... 1137

The FIRST fail (image above) was:

TEST ----- HC --------- CO -----------NOx
15MPH ... 236 ........... 3.00 .......... 1475
25MPH ... 237 ........... 2.97 .......... 1365

Then, I did a compression test, determined the vehicle was "reasonably fixable", and pursued that route. I installed brand new injectors (including new seats, Orings and seals), rebuilt WUR, new O2 sensor, adjusted the Aux Air Valve (to close at lower temp), and adjusted the mixture CO screw using an oscilloscope attached to the ECU to get the mixture "on the money".

I then returned and did a smog pre-test, with numbers approximately like this:

HC -------- CO ---------NOx
185 ........ 2.00 ........ 1260

Yuk. Ken said he could spend some time attempting to adjust (for a significant fee) to see if he could get it into compliance, but he expressed doubts, as there was still a slight misfire. As it happens, he was unable to get it adjusted to compliance, and he gave the car back (no charge, as he was unable to correct it - he's been very helpful in this process).

So off I went. In the next set of repairs, I grounded the O2 sensor to the chassis, replaced the fuel filter, replaced all plugs, plug wires, cap and rotor, replaced the Air filter, and finally, I rebuilt the fuel distributor. Micture adjustment this time was using a duty cycle meter attached to my ECU mod (that allows for straight duty cycle measurement with no oscilloscope).

With all of this the car was running *excellent*. I took it back as per the start of this post, and the approximate pre-test numbers were:

HC -------- CO ---------NOx
210 ........ 0.95 ........ 1800

Well, I got the CO down. LOL. :banghead:


Based on THESE results, it now looks like

A) The car is now TOO lean.

B) My Catalytic Converter is failed.

The cat is about 8 years old - but for many thousands of miles, has been pummeled with a too-rich mixture and misfires. Contributing to my feeling that the cat was bad was that the central pieces of the exhaust seem to rattle.

My current cat is welded in place, so I'd need to saw it and weld in a new one. While I've never welded before, I think I could climb that curve. But I also need to get this car done, and due to holidays and other issues, I couldn't get to my DIY garage till saturday, PLUS no reasonably priced outlet had my cat in stock - all places with decent prices like Autozone had them as special order (and this for the universal California version).

So I decided to go to a muffler shop. Checking YELP and calling a couple places narrowed it down, and one place I called even referred me to another on my list to check - and that's where I ended up, at ATLAS MUFFLER on Santa Monica.

The owner Nazo is *extremely* friendly, helpful, etc. etc. I definitely recommend. He also replaced a failing donut (which was actually making the biggest rattle). Total with tax was $320. Breakdown was $200 for the Magnaflow cat, $85 for labor, $15 for the donut, and $20 in tax (hey, don't you think California should WAIVE taxes on smog equipment??!!!!)

After cutting it off, I took these images of the old cat:




The exterior has signs of overheating.

Looking at the front and back of the old cat, it doesn't look "that" bad - BUT - you absolutely can not see ANY light through it. Looking through it, it seems very clogged, as I suspected it would be.

I'm surprised the car even ran as well as it did, but there was the leaking donut that was partially melted, that was probably reliving some of the back pressure (LOL !):

Before the new cat was installed, I looked through it - it is actually hard to see *much* light through these, but there was definite light in the new one, as opposed to zero light in the old one.

Welded in:

Running, the engine idle is a nicer hum. With all the recent repairs, I can chirp the tires again on acceleration!


In preparation for smog (tomorrow or Friday), I am also:

1) With currently about 6 gals in the tank, adding a full an of seafoam to burn out any remaining carbon deposits. I haven't done that since repairing the fuel distributor, and cylinder one may still be gunked up with carbon. Will be doing extended freeway tonight, and tomorrow before testing.

2) Adding a gallon of antifreeze. With some of the work I've done over the last month, the water ratio may be too high. I've read that this can lead to localized steam bubbles around the cylinders, causing higher combustion temps (causing an increase in NOx). I do need to do a full flush and new radiator, but can't this week, so I am hoping the additional coolant will be enough.

3) Adjust CO mixture screw. I had set it for straight 50/50, favoring the lean side (the DMM would fluctuate 49-56%) I reset it to favor a more rich default mix, so that the DMM is fluctuating between 42-50%. Now, at 2500 RPM (no load) it drops to 25-35%, indicating the Lambda is trying to lean it out more. My hope is that this results in a slightly richer mixture overall, to help lower NOx. For the record, this involved turning the screw about 1/64th of a turn clockwise.

In other words, making the Lambda system work harder at leaning *should* result in a slightly richer mixture, as the ECU trim limit is approached. We'll see at the smog test.

Beyond this, I am now about at "the end" of what I can do. The one other possible issue is the timing chain (70K miles on it) if it has stretched too much, causing the valve train to be out of time, that *might* be a cause of some emission problems.

I hope not. After everything I've done to THIS point, I want to put off the radiator and all other issues till NEXT time. !!!

Smogging tomorrow or Friday - to be continued!


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