C230 K/M271 hard to start & extreamly rough idle

[Rogerfl]

i need help diagnosing a 2005 C230 Kompressor (M271 Engine) that is hard to start and will not idle. It runs smooth with reasonable power when the RPMs are over 1500. It dies if you let it idle when cold. Will idle but very rough when warm. Starts easy after a stater fluid spray.

It is throwing codes P0171 (lien trim adjust limit) and P0300 (misfire) all the time and occasional throwing codes P0304 (RPM) and P0444 (Evap purge circuit open).

Compression test results:
dry: 95-100 PSI all cylinders
wet: 110-115 PSI all cylinders

No obvious vacuum leak. Plan to do smoke test tomorrow.

Just purchased the car, so do not know the history. 140,000 miles. The body/interior indicates the car was well taken care of. I seems like a large vacuum leak causing fault codes. I'm at a loss to explain why it runs so good with the low compression.

any help is greatly appreciated.

- Roger

 

[markjay]

The common faults for the M271 are timing gear failure, split vacuum hose under the air filter box, clogged engine breather, and leaking camshaft position sensor allowing oil into the ECU via the wiring loom.

The timing gear failure is the most critical one, so check that first.

But if course, there are other possible causes e.g. failed sensors, fuel injector issues etc.

 

[Rogerfl]

I removed the valve cover, checked the timing chain which is tight and looks like it has been changed. I used a small inspection camera to examine the piston tops and they have suspicious indentations at areas where the valve might contact the piston. The suspicious area is covered with carbon so any impact is not fresh. the cylinder walls are crosshatched and there is no signs of scoring. the camera does not allow me to look up, so could not inspect the valves.

I have never seen the top of a good piston on this engine so I have posted a few pictures hoping someone can analyze the attached photos and let me know your opinion.

Thanks!
- Roger

 

[paulr2006]

Not an expert on this engine but looks to me like deliberate moldings in the pistons to accommodate the valves

 

[Rogerfl]

I agree. I have found photos of new pistons for this engine and they look the same. So no evidence of valve-piston contact.

So its unknown what is causing the low compression readings. I pulled the valve covers, positioned the crank shaft to cylinder 1 TDC, and observed the cam timing marks. it appears that one of the cam's could be off one tooth, but its very close and I'm not sure. See the attached photos. Even if it is one tooth off, not sure that would be enough to explain the low compression.

Any thoughts would be greatly appreciated.

 

[paulr2006]

If it's service history is unknown it may well have done extended mileage between services which could equate to cylinder/ring wear which would of course show up as low compression.