W203 C180K Coupe running issues and solution

[Retroenduro]

Hi all

I thought i would share with you my experiences with my wife's C180 coupe and a niggling problem it 'used' to have which MB couldn't seem to get to the bottom of. Im posting this in the hope that it may be able to help out some fellow MB owners.

So my wife bought her 2002 C180K coupe years ago and it always had this quirk of occasionally running really badly. The idle would be as lumpy as anything and power would be down...but then turn it off and on again and it would be fine for a bit before eventually doing it again. She took it back to MB under warranty and they had no idea what was causing it...they changed the plugs..worked fine for a year..did it again. Then they changed the coil packs again with the same re occurrence. They even changed the timing chain etc and the problem kept coming back...the thing that got them was that every time they plugged it in to the diagnostics it would spit out meaningless codes.

Anyway after we got together we were out on a drive when it started doing it again. To me it felt like a dead cylinder so the first thing i did was to gently pull disconnect each coil pack whilst the engine was running until the one i disconnected resulted in no change to the engine (the others would theoretically kill another cylinder and would make the running REALLY rough). OK so did this and worked out it was cylinder 1 that was not firing...

Next i pulled out the coil pack - tested OK, had a look at the spark plug and noticed a fair amount of rust...including what looked like carbon trails on the insulating material...AHA! so it seemed that the voltage for the spark was earthing across the insulator and not firing the cylinder. As soon as i cleaned it up it worked perfectly...

So anyway why did the arcing start to happen? well a month or so later on a cold damp day it started to do it again. I was at home this time so i got out the tools and pulled the coil pack off. Now before pulling out the plug i had a quick peek and found the whole area in which the plug sits under water! Originally i thought it may have been a head gasket leak as where would that water come from???? but i got some water out and it was fresh...not coolant. So again how did the water get in there....

I was scratching my head when i looked down and saw the upturned plastic engine cover on the floor, you know the nice flash one with MERCEDES BENZ all in nice lettering on it...the exposed plastic bits on the underside were covered in condensation and the foam was damp! So this is where the water came from! I can only speculate that on damp/cold days condensation was forming on the underside of the plastic cover. Now when the car was parked facing downhill this condensation would run and the drip, drip, drip into the sparkplug well on cylinder no 1. thus filling it with water, causing arcing of the spark and a dead cylinder! I have since removed the cover and have not had the problem since....

if you are having a similar problem see if removing the cover and cleaning up the no.1 sparkplug works.

However..i would like the cover back on as it looks nice so any suggestions on how to stop the condensation forming on it would be gratefully received!