Mercedes C200 2003 - Misfire problems

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Sat 4 Aug 2007 12:56
Mercedes C200 2003 - Misfire problems - John S
Friend?s car (75k miles) is suffering an intermittent fault. Brought to idle a few miles after a cold start it misfires badly. EML sometimes illuminates. Misfire won?t clear until car is switched of and restarted, after which the problem will not occur for the rest of the day. In addition the EML sometimes illuminates when driving without causing any obvious problems with the car?s running.

MB dealer charges £250 for diagnostic and says ?unknown? fault code, finds one cylinder slightly low on compression (3 at 11 bar, one at 9bar I believe) and suggests fitting new cylinder head for £3k. Friend leaves MB dealer??..

Specialist confirms the above (for free), including unknown fault code. Thinks problem may be coil packs, but these show up as OK under test. He offers head repair for much more reasonable price, indicating it may be a sticking valve. Friend is going along with this. He?s going to keep the car for a while; reasons a burnt out valve won?t get any better and it eliminates one possibility.

We still think it may be electrical, but thought coil packs would tend to fail completely and not intermittently. Why does it happen only once after a cold start? Any suggestions greatly appreciated.

JS
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Sat 4 Aug 2007 13:15
Mercedes C200 2003 - Misfire problems - Screwloose
JS

Are you 100% sure that it's got the correct oil in it?
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Sat 4 Aug 2007 17:58
Mercedes C200 2003 - Misfire problems - John S
Screwloose

No reason to believe otherwise. MB/specialist service history. Difficult to imagine oil could be so far wrong as to cause problems like this.

JS
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Sat 4 Aug 2007 18:04
Mercedes C200 2003 - Misfire problems - Screwloose
JS

You'd be surprised.... A 10/30 instead of a 0/30 is all it would take.
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Sat 4 Aug 2007 18:11
Mercedes C200 2003 - Misfire problems - elekie&a/c doctor
Before you go any further with this ,I would suggest that somebody checks the engine management control unit multi-plug wiring connectors.It is fairly common for these to fill up with engine oil due to hydroscopic action within the engine wiring harness from the engine sensors.This can cause all sorts of erratic running problems.If this is ok ,then a new set of coils may be the answer even if they seem to check out correctly.A 3k head overhaul?I am not convinced.hth
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Sat 4 Aug 2007 18:34
Mercedes C200 2003 - Misfire problems - 659FBE
I suspect our ever knowledgeable friend Screwloose has in mind the possibility that the hydraulic tappets will not operate properly if an oil of too high a viscosity is used.

A low compression is always a cause for concern if an engine is not running evenly and if the oil specification were to be incorrect, it would be a cheap fix. Valve seat erosion is rare on MB engines, but I've seen a few head gaskets with pushed out firing rings...

659.
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Sat 4 Aug 2007 18:43
Mercedes C200 2003 - Misfire problems - Aprilia
If this is the M111 engine then anything from a 0W-30 to a 10W-40 should be OK, semi- or fully-synth. Recommendation is 5W-30 or 10W-30 for UK.
I would tend to go with the coils being first suspect.
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Sat 4 Aug 2007 19:50
Mercedes C200 2003 - Misfire problems - John S
Thanks all. I'll pass on the comments. I guessed what screwloose had in mind, but the car actually runs very smoothly when it?s ok. With relatively limited compression deterioration on one cylinder, that?s perhaps not surprising. I?d also expect the hydraulic tappets to play up on start-up when viscosity?s at a maximum, but it starts without any tappet noise. This one typically ?plays up? 8 miles from home, when it?s warmed up, which makes me think electrics, sensors, ECU connectors etc and certainly those coils, despite the check. Given the ECU fault code, the coils must be suspect. I?ll pass your comments.

Yes, MB?s £3k head replacement indicates they have lost the art of repair, valve grinding etc. and takes the art of sub-assembly replacement to new heights! Luckily, the indie maintains the repair tradition.

Not sure of the engine designation, but it's the 1.8 litre supercharged unit.

My friend is going to go with the head removal, so that will check the gasket too. If he gets a resolution to the problem, I'll report back.

JS
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Sat 4 Aug 2007 20:02
Mercedes C200 2003 - Misfire problems - Armitage Shanks {p}
Any prolonged misfiring may have damaged the cat converter - I hope not obviously
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Sat 18 Aug 2007 10:47
Mercedes C200 2003 - Misfire problems - update - John S
Update - haven't seen it myself, but I'm told that the head came off and one inlet valve guide was found to be loose in the head. The associated valve and seat are both slightly burned, hence the low compression. The theory is that this guide moved during warm up, held the valve off the seat, and caused the 'misfire' - actually a spell on 3 cylinders as that one lost compression - and the consequent burning of the seat. When the engine stopped it went back into place. So, just as well this problem is sorted. Head is away for repair. We shall see......

JS
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