CLK 200K Misfire

[lyrobertson]

Hello
First post so please bear with me!
I have a 55 plate CLK 200K, 44K miles. A few months ago my engine management light came on, was going up hill, about 4000rpm, then loss of power and the car drove like a pig. Was all fine again after i switched the engine off. Happened a couple of other times.

Went to Merc dealer who told me that it was likely to be 'sticky' values and would need total engine stripped down (not cheap!). Fault code was misfire on cylinder 2.

He swapped over cylinder 2 and 3 just to check it wasn't anything else.
Car then ran fine for 3 months, no problems, high revs, uphill, flats, perfect.
Then fault back again yesterday.....

I just can't understand why if it was a mechanical fault it went away for 3 months??

So we have bought a replacement coil pack to try that, but we don't know which cylinder is number 3 (where hopefully a faulty coil pack is now sitting and not an expensive new engine) Is is just as simple as the third one from the front, or is it in reference to the firing order?

Any help or advise would be gratefully received.
Many thanks
Lynne

 

[mebs]

HI
If you dont mind me asking how much have you spent so far in trying to resolve this issue? and did you see the printout on star diagnostics

 

[lyrobertson]

Hiya

Thankfully spent nothing so far, but no I didn't see the actual print out. They literally swapped the coils over from 2 to 3, as compression test came back fine, so they couldn't 100% confirm it was a value problem.

If when I go back and they run the diagnostic again, and the fault has moved to number 3, it might not be the value, but if it is still in number 2, then it isn't looking good.

I am just looking for a bit of advice as it all seems a bit vague to me and not very logical, as the car runs perfectly.

All very strange.

thanks for getting back to me.

 

[Shude]

My 1998 w202 c230k did something very similar to this for about 18 months with various attempts from different workshops to resolve. Essentially if you drove it VERY sedately then it was fine but if you went anywhere near the gas pedal on a hill or tried to accelerate anything more than gently it would misfire on one cylinder, lose what felt like about 50% of the power and the cylinder would continue to misfire until the engine was switched off.

It ended up being the rubber boots on the bottom of the coil packs (may have only been one of them) but during diagnosis I replaced both coil packs , MAS, some wiring and several other items.

 

[grober]

Cylinder position on a straight 4 are normally numbered from the front 1-2-3-4 at the rear. (note:- that's not the firing order) check all your flexible inlet pipework from the compressor etc is secure, but Shude's rubber boot suggestion may well be correct. The problem will be if moisture gets in there causing a Breakdown in HT insulation losing you spark at the plugs. A quick spray of water dispersant such as WD40 will effect a temporary cure and help pinpoint the problem. Permanent cure would be new boots as suggested.

 

[lyrobertson]

thank you Shude and Graeme for getting back to me.

My fault is exactly as Shude described. We changed the coil pack today in cylinder 3, and no joy, fault back when under acceleration going up a hill.

Very interested to learn more about the rubber boots. Could you please let me know if you are referring to the plastic tube which is attached to the square coil that connects to the spark plug, or is this something totally different. If you could point us in the right direction it would be a massive help. We can't seem to see anything made of rubber?


Thank you
Lynne

 

[Shude]

My fault is exactly as Shude described. We changed the coil pack today in cylinder 3, and no joy, fault back when under acceleration going up a hill.

Very interested to learn more about the rubber boots. Could you please let me know if you are referring to the plastic tube which is attached to the square coil that connects to the spark plug, or is this something totally different. If you could point us in the right direction it would be a massive help. We can't seem to see anything made of rubber?

I don't know where they are but I actually have the old rubber (could be plastic now you mention it!) tubes in a box somewhere as I don't throw anything away! They were only about £8 each and were fitted in under 10 minutes IIRC which is mildly annoying after literally 18 months of mystery.

Swapping to a different cylinder did improve things for a short while but there are so many variables and if things are loosened, tightened back up again etc then problems can go away temporarily but usually come back. If I can find the rubber/plastic boots/tubes then I'll take a pic of them for you. I did find the coil packs earlier (which prob didn't need replacing) and also the original MAS (which had done 160k miles and prob didn't need replacing either!) so I can't be far from them.