PeachParts Mercedes-Benz Forum - 2002 E430 misfire diagnosis

Since I got the E430 in 2005 I haven't been as active on this board. Compared to the W124 cars, there is little if anything needed. This car has been one of the best I've ever owned. But, now it is getting up there with 127,000 miles and little problems are popping up. So I thought I'd write about my most recent issue in hopes that it will help the group if someone has a similar issue they are chasing.

The car had been running well. No issues at all. I went to start it to drive home from work and it was running very rough and the check engine light "CEL" went on. I drove home and got started digging in. I thought I'd pull a few plugs and look for a sign that one cylinder might not be firing, like a wet plug. I pulled the front two and they looked fine. The task is a little daunting. We have 16 plugs, wires and 8 packs of coils with 2 in each pack.

Then I had a better idea and I decided to disconnect the coil packs one at a time, basically dropping one cylinder at a time while it was running to see which one was out. That helped. As I unplugged each coil pack, the missing got worse, except for the front passenger cylinder #1. OK! There was no change when I unplugged that one. We are getting somewhere!

I used a spark tester tool (Pep Boys, $6) that plugs between the wire and the plug to see if there was spark. There was spark! So I figured the plugs on that cylinder were bad and I replaced them. Nope, that cylinder was still missing.

OK, next step, I unplugged injector #1, no difference. I unplugged injector #2 and it ran worse. I swapped injector 1 and 2 and the problem moved to cylinder #2. Got it! Bad injector. I ordered one ($120) and installed it yesterday. Done! The car runs great.

A couple of notes:

I also replaced the fuel filter. I don't know what fouled that injector, but I want a fresh start.
Although I had the #2 injector swapped into the #1 position I put it back to #2. I figured I want the new one up at the front. It is at the end of the fuel rail and most likely to get water or other crud.
I disconnected the battery to clear the CEL. Don't forget to have your radio code handy and also you will have to synchronize your windows and sunroof.
Remanufactured injectors are around $40. I went with a new Bosch injector. I don't know if the reman is the same quality so I didn't risk it.

I hope this helps someone. Swapping the injector is easier said than done, but I am guessing I saved a huge amount of money by taking the time to figure this out. Thanks for reading this!!