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.
DIAGNOSIS PART ONE
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.
As such the FIRST STEP is a COMPRESSION TEST.
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.
READING COMPRESSION and RESULTS
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).
THE FINAL FIGURES
1 - 143
2 - 145
3 - 147
4 - 145
5 - 135
6 - 145
7 - 142
8 - 150
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
wires was split:
# 1 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.
END OF PART ONE