1980 450SL Engine and Smog Troubleshooting and Repair - Mercedes-Benz Forum
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post #1 of 27 (permalink) Old 10-15-2014, 01:20 AM Thread Starter
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Date registered: Jan 2009
Vehicle: 1980 450SL named Freya. 202,000mi
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1980 450SL Engine and Smog Troubleshooting and Repair

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)

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! 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.

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Last edited by Myndex; 11-29-2014 at 02:33 PM.
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post #2 of 27 (permalink) Old 10-15-2014, 02:20 AM Thread Starter
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Vehicle: 1980 450SL named Freya. 202,000mi
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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 ( 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,

Last edited by Myndex; 12-02-2014 at 09:05 PM. Reason: Update some information on lambda systems.
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post #3 of 27 (permalink) Old 10-15-2014, 05:12 AM Thread Starter
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Vehicle: 1980 450SL named Freya. 202,000mi
Location: Hollywood, Ca.
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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......
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post #4 of 27 (permalink) Old 10-20-2014, 03:34 AM Thread Starter
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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 dykes 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.
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post #5 of 27 (permalink) Old 10-22-2014, 07:04 AM Thread Starter
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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.

Last edited by Myndex; 11-27-2014 at 03:07 AM.
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post #6 of 27 (permalink) Old 10-22-2014, 08:42 AM
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Reading with interest!

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post #7 of 27 (permalink) Old 10-22-2014, 06:28 PM Thread Starter
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Originally Posted by SuedeGopher View Post
Reading with interest!
Thank you

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.
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post #8 of 27 (permalink) Old 10-25-2014, 12:03 PM
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Very informative thread.

Last edited by dgosh28; 10-25-2014 at 12:13 PM.
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post #9 of 27 (permalink) Old 10-26-2014, 10:20 AM Thread Starter
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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!!!


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post #10 of 27 (permalink) Old 11-10-2014, 07:29 PM Thread Starter
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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.
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File Type: jpg BadStud.jpg (29.2 KB, 2859 views)
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