M119 92 500E engine miss
 

I bought a project 500E with 157k miles. First thing I'm tackling is a slight engine miss at both idle and at speed. You can feel it at idle sitting at a red light, and at speed at high RPM.

I have inspected the plug wires and they are recent and look fine. They are Beru brand. I pulled one plug and it did look somewhat worn (grey powder all over anode). I was able to pull one plug wire at idle and have the miss not change, thinking I was on to something. Then I went and pulled another one, and it did not change either.. I am thinking this is a miss across all 8 cylinders.

I am wondering if this is a common problem/common fix. Any help appreciated!

check the coil output you will need a tester for that, and then look at the distributor caps and rotors they may be bad, the engine wiring harness is also a good place to start

I'd also consider replacing the main engine wiring harness, if you can't verify that it's been done in the past few years. This part can be purchased wholesaie for around $550, and is a several-hour DIY job which is not rocket science.

I had an occasional miss that would come up at idle, particularly when the car was warm. The car would shudder when this would happen. Replacing the harness removed it for me.

If you don't know, this harness is one of the only known weak points of these cars. They were made out of a biodegradable wiring insulation during the years 1993-1995 for all MBs and age and heat (especially with the packed 500E engine compartment) tends to make the insulation dry up and crack, or worse flake off, causing wires in the harness to short out/together. This leads in bad cases to all sorts of weird running conditions, or as in my case merely a mild miss. I was shocked to see the degradation in the harness of my 85,000 mile 1994 model.

You can see far more about this issue and other problems at the mecca for 500Es, which is at http://www.500e.com

Cheers,
Gerry

Thanks Gerry. Is there any specific place to look for insulation deterioration? I'm going to rip the car apart today.

I emailed the admin over at 500e.com, I signed up for my account "turbodiesel" but never rec'd a conformation email.. and I am unable to post. If you can get ahold of him and let him know, I'd appreciate it.

Hmm.. I think this could be the cause :)

http://207.44.234.41/500e/IMG_5643.JPG

http://207.44.234.41/500e/IMG_5644.JPG

Looks like a bad engine wire harness to me!

Replaced the harness, symptom persists.

Slight miss/shaking engine at idle. I did notice one time while playing around this morning that my accelerator pedal had to be pressed further down to get a throttle response.. all is back to normal now. The ABS and ASR lights come on at random now when you start the car.. 50/50 chance if it coming on at startup and they don't go off until you shut the car off.. I don't know if this could be a hint??

A 500E beater - wow never thought I'd see that one.

M119's are very hard on distributor caps and rotors - Pull them off and take a look for carbon tracks. Do you have any records with the car? The ETA (Electronic throttle Actuator) frequently fails at 125-150K miles. This will cause check engine lights normally but I would suspect it could also throw codes in the ASR system as well.

You might want to also check the fuel pressure - my cousin had a 400E that had a miss at idle and seemed to be running rich. He found the fuel regulator had failed and the rail pressure was over 100PSI.

Update.

I inspected the caps and rotors, slightly corroded. Cleaned them and replaced. I removed the Electronic Throttle Assembly and took it to my friend who also rebuilt my wiring harness to inspect.. he could find nothing wrong with it electronically. I re-installed it and now the car has only 1/2 throttle response and still misses.

After building a code reader/clearer I found 11 codes (most from bad harness, I assume). I cleared all of them but only two come back now.

Pin 7 (EA module) = Code 14 (Closed throttle position contact switch (S29/3) )
Pin 6 (ASR module) = Code 30 (CAN data line to EA/CC/ISC module (N4/1) )

Any ideas? This thread is similar to my problem.. http://www.500e.com/forums/showthre...&highlight=mode

Ideas?

check out . .
 

. . my page's MENU#24 for alot of similarities. How did you test the ETA off the car?? The DTCs that have returned are a definite indication of a bad ETA.

But, that won't fix the hesitation. Have you "tapped" the fuel distrubtor (FD)? Try that with every port. Mostly likely it's the 'stuck' port in the FD?

Jim, your page has been invaulable to me in diagnosing this car!

My friend checked the wires, checked the resistors, and checked all contacts to make sure there were no shorts or opens. He also inspected the slide pot and cleaned it. I suspected this because of my ASR & ABS light. Some have said after replacing this, the hesitation and miss at idle dissapeared.

How do I tap the FD module? Thanks for your help and your webpage!

I've done it using . .
 

. . a small ballpien hammer, tapping each port. My tech showed my that and many times, it fixes a stuck valve.

So the 'testing' was just more like cleaning, etc. With 150K on the Ref Pot, it's probably history. Check MENU#24 for some sources to re-furbish for a reasonable cost.

$1100+ tax at the dealer. Beckman could probably do it for $600 or so.. but they have never seen my exact model number so they will have to double check.

Another interesting note, he says the majority that come in check out OK.. it's usually the V12 actuators that are bad. He said if your wiriting is ok (which it is) then it is most likely alright.

What else would cause the CAN bus to not communicate to the EA? I don't think it has anything at all to do with the upper wiring harness (which was just rebuilt).

I also get the idle switch error, which is located at the top of the acclerator pedal. I get 1000ohms off idle, and infinite (open) at idle. Is this normal or should it be shorted off idle?

I serviced the ETA, works perfectly now.

There are no codes in any computers but the car still runs rough and smells very rich. There is also a high RPM miss, say a WOT downshift at 80mph, you can feel the car bucking. An oxygen sensor is the next item to be replaced.. any more ideas?

I'm curious . .
 

. . what did you do to 'service it'?? Did you say that the internal wiring was ok?? How did you determine that??

Cleaned/lubed all gears. Cleaned contacts and brushes, Bent brush arms up so they make a firmer contact with the pads. Checked the resistors and wires for opens or shorts. It's a pretty complex little device, not for the faint of heart.. I had it in about 30 pieces.