PeachParts Mercedes-Benz Forum - How Screwed Am I? (E420 w/ pictures)

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I don't think anyone has argued not to replace it - only that if it's not a present problem replacing it now is a personal choice. Certainly an engine fire is horrific but that doesn't address the probability of it happening. There have been very few wiring harness related fires, perhaps odd but true, and the few that I'm aware of were all 104 motors. The likelyhood of going from running fine to fire without any forewarning is even more remote. Forum folks tend to be very free with other people's money but in the real world these preventaive things generally don't get done on cars without substantial market value - because the risk of doing it and not doing starts to equalize. Different analysis five years ago. Again, it's a personal choice - the owner has to consider the condititon of the car, their long term committment to it, the value they put on reliability, etc.

BTW, the story of the $2100 new ignition control module part is suspect - theoretically possible but the part is around $800 list, available for less new and $100 to $200 used which in my mind would cast some doubt on the diagnosis as well.

That's what Phil charged me.

Thanks for the feedback!

It's great to hear from everyone and it sounds like a pretty unanimous consensus on the approach to the problem. I think my biggest fear is the expedited deterioration due to -10 degree winter weather consistently stressing the wiring in the upcoming months. The shopping for the harness has begun.

I just wanted to post a follow-up on the this topic. I replaced the wiring harness yesterday and the worst was true. After slicing open the sheathing it was crystal clear how bad the problem actually was. The usual cracking and disintegration of the insulation in the harness was everywhere. (maybe I'll post a picture of the unit but I'm sure everyone has been there and done that)

Thanks again for the input on the replacement!

Please post, I have not seen.

It is not a pretty sight. Just look at that fine German quality.

This same problem happened to Volvo back in the mid 80's. My 1986 740T had the 'biodegradable engine wiring harness' and the insulation turned to dust. I replaced the harness which cost me $300. I should have repaired it for $50, or so.

don't forget the harness to the starter they were affected too.

Did this fix your idle problem?

Idle is a little bit smoother (especially in the morning when the engine is cold) but I'm still pulling CEL codes. The EGR valve is a big one (Code 5) that may have a play in the idle as well as a good cleaning of the MAF (Code 4). I'll post pictures within the next few days and keep everyone posted on the idle with the EGR connection and MAF cleaning.

Also, from what I've researched, the secondary harness (starter, o2 sensors, etc...) isn't exposed to the high temp engine heat so it doesn't break down as quickly? Does this sound correct?

Pictures of the harness...