M119 92 500E engine miss

[turbodiesel]

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!

Originally Posted by turbodiesel

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

[gerryvz]

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

[turbodiesel]

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.

[turbodiesel]

Hmm.. I think this could be the cause





Looks like a bad engine wire harness to me!

[turbodiesel]

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??