I started this over on the "new guy" thread, but I have some detailed questions and was directed here. I've had an '84 300SD and an '86 560SEL so I'm a little familiar with MB.

This is my son's first car, a W202 1994 C280.



It has only 107,000 miles and is clean, tight and rust free. Other than the obligatory weeping headliner, the interior is sparkling clean. It had a disintegrating engine bay wiring harness and the PO replaced it as well as the trans harness. He also replaced spark plugs and did a few other things. Supposedly he is a certified Mercedes tech, but a little young to be too experienced.

It still has some ignition issues and I'm not sure if it is more than I want to tackle. I work in a body shop and have access to a scanner. These are the codes:



Symptoms are rough, bouncy idle and rough acceleration that increases as the car warms up. Car rides smooth as glass with foot off the accelerator, but as soon as I give some gas, I get a vibration. Feels like a cylinder or 2 is not doing its job. It gets pretty bad after 1/2 hour drive and the power dies to almost zero, but turning off the ignition and restarting clears it up until it drives a while again.

Climate control baffles do not operate nor do the locks, so there is likely a vacuum issue. I'm not 100% sure the guy that replaced the harness did not knock something off. I do not have a smoker.

Anyone know of a good ole MB guy in central NJ?

UPDATE: So I just read this over on Wiki and it sounds exactly like the issue I'm having:

<i>Whilst the M104 is known to be a reliable engine, there were some technical issues with smooth running. The wiring loom which passed from the Idle Speed Control unit (an electronic box situated in the engine bay) to the ignition coils (housed on the top of the engine) was enclosed under plastic covers. High temperatures were experienced in this region. In addition the plastic insulation was a type which degrades with time and heat.

The ignition coils provided current for two spark plugs each. A system of “Wasted spark” was used where one coil powers two spark plugs. But the coils were still subjected to a high heat zone.

Idle speed problems could be experienced if the coils / wiring breakdown damaged the Idle speed controller. This manifested itself with engine not idling at the correct rpm, normally 667, but hunting could be experienced with the engine ranging up to 1200 rpm. If the coils become damaged they may still operate at low engine rpm normally, but at higher engine loads the coils can break down resulting in engine power loss as the number of power producing cylinders reduce from six to four or even in worse case scenarios two.

Wiring loom upgrade kits were made available with upgraded insulation to resist the heat.</i>

I'm thinking, and feel free to correct me if I'm wrong, that the high O2 sensor voltage is due to the fuel mix being too rich because of the misfires and C1 and C6. Since the wires and plugs are new, I'm leaning (pun intended) toward bad coils in those cylinders.

It also looks like I might need a new crankshaft position sensor. It is a wearable part...no?

Don't have a clue what the Down angle control ignition output stop short to ground is.

Thanks for any suggestions.

 

Thanks! But it's easier said than done. The car has an OBD2 plug under the steering wheel, but the only information you get from that is all the other adapters and cables you need to hook up under the hood. It's a rather Rube Goldberg affair that takes 1/2 an hour to do. It's a lot of favor to ask a tech to stay that long after work.

 

No run around. It was a mechanic from my shop that scanned it. I watched him do it. 2-3 cables and a bit of "key on, key off". It's just more entailed than OBD2 compliant cars. Most shops around me won't touch it. They can't be bothered. I found an nice father/son Mercedes shop in Tinton Falls, NJ that will look at it on Monday.

 

Do my eyes decieve me or does the color change between front and back doors?

Any and all wires subject to heat are to be suspect in a '94.

I had a '93 W124, had no peace until I replaced top harness and ETA. Even then I got issues from bottom harness, but at least it ran well.

 

Update:

So I brought the car over to a German car shop in NJ. It's a father/son team where dad works on the older stuff. Mine qualifies as older stuff.

He actually took on the challenge and stayed with it until 10PM trying to figure out the issue. Coils, plugs, wiring all good. It runs great at first, but as it warms up it starts loading up with fuel causing misfires. O2 sensors are "pinning the needle" which confirms it's running rich.

He said it could be in the ECU, which is more plausible since the old wiring harness had a few shorts in it. I called my local MB dealer and he gave me the part number, 0185456632. Luckily, I found one on ebay for $87!

As coincidence would have it, my son called me and said "there's something wrong with the car". He stopped at a light and the car wouldn't move when he tried to accelerate. The engine was running, just no power. He turned off the key and restarted the engine and it ran fine, so something seems to be resetting. I told him to get it to my house and we'll install the "new" ECU.

The mechanic said it was 50/50 whether a used one would be plug and play. My car is right on the edge on when cars switched over to ECUs that need to be married to the car.

Well we put it in and lo and behold, it started right up. Lots of power. Engine revved nicely. Interestingly, the part# on the one that came out was an 013.......#, hum.

But fast forward one day and there is still a miss, although not as bad, and it's still loading up with fuel, also not as bad. Crap. The bewildering thing is that it appears to be intermittent. Sometimes it comes to a stop and the engine will run rough, other times it's smooth as can be. Driving it for 30 minutes or more seems to bring on the trouble.

Could it be a fuel injector or two dumping fuel as it warms up? Maybe an o-ring kit is in order? Anyone have any experience with reman fuel injectors?

 

Yeah, it looks like the back door had some paint work. It doesn't match the front door or QP.

The previous owner took the hit and replaced the engine harness and trans harness. The shop I took it too checked it out. Seems like it's a common to find the wrong harness on these cars.

 

I just came across this thread. It sounds like my issue.

https://mbworld.org/forums/c-class-w...-misfires.html

Fuel pressure sensor...oh boy, if that's the only issue!