06 C230 Sport - Engine missing w/o any CEL
 

Hi all,

Looking for any help with possible causes. My wife's C230 Sport was running just fine till 2 days ago when it started to run rough in the middle of an 80 mi. jaunt, like it was skipping a cylinder, but intermittently, not in a consistent way like if it had a bad coil on one cylinder. The missing is occassionally accompanied by what sounds like a muffled backfire into the airbox (don't know if that's even possible w/modern engines) and also occassionally what sounds like a muted mechanical "clunk". Not positive whether it's from inside the engine or possibly outside from the engine reacting to the miss. The thing is, there's no Check Engine Light that would indicate that the ECM is aware of the fault.

I would appreciate any suggestions on troubleshoooting this problem.

Thanks in advance.

I’d suggest to take a look at the plug wires and connections.

Has the balance shaft sprocket been replaced yet? How many miles on the spark plugs?

Use a scan tool and look at the miss fire counts. There is a certain threshold that must be met to trigger a code / light and you might be just under that.

An intake pop signifies a lean mixture / intake valve hanging open ( like a broken valve spring ) / ignition timing issue.

Yeah, that was one of the first things I checked. Everything looks ok and I jiggled, wiggled, and tweaked things to see if it made any difference. No luck.

Thanks for the suggestion, though.

Not since we've owned it from about 50k mi. and it's now at about 110k mi. Are these a problem on this engine? I've heard about it on the E350, but not the C230.

If the chain skipped a tooth on the sporocket wouldn't you feel a vibration all the time? Not the case with the current problem.

Any idea what the job entails? Any special tools needed?

The plugs were replaced about 30k mi. ago.

Thanks.

I'm borrowing a scan tool from a friend this weekend to check out what's going on inside. I'll look at the misfires. Does the computer store this value, or only check it while the engine is running?

Would the scan tool show the lean mixture or ignition timing issues, if present?

Can you (or anyone else) recommend a good, not overly expensive scan tool that that will interface with my laptop?

Any easy way to check for a broken valve spring? Also, are these interference or non-interference engines?

Thanks for the tips.

Miss fire counts are active when the engine is running, they get reset / reduced in number after a certain time period and clear when the engine is off. The strategy is manufacturer specific so you would need a service manual to get exact details.

There is a long term and short term fuel trim that would indicate the computer is compensating for lean or rich mixture. There is usually spark advance data on the scan tool however this would only be useful if you knew what it should be. This is only what the computer wants the advance to be not necessarily what it actually is during a problem.

Define " overly expensive ". The $ is in the software not the hardware. For perspective, last I checked a real MB scan tool ( Xentry ) is something like $ 20,000 plus $ 6,000 per year to keep current. If the subscription isn't kept current, the scanner bricks.

Contact the guy in post 12

https://www.peachparts.com/shopforum/tech-help/399966-w211-air-suspension-pump-replacement.html

I don't know if these are valve benders or not, this only comes into play if the a timing chain / belt hops multiple teeth or breaks

The only way to check for a broken valve spring is to remove a valve cover on the side that is making noise.

All 06 and part of the 07 m272 production run have the bad sprocket. Your 06 c230 has the same m272 as the 350 just smaller bore and stroke. It's not a matter of if but when. It's an engine out job.
Mercedes Benz balance shaft engine issues. How to check by VIN. M272/273

Its a balance shaft issue when code 1200 and 1208 appear , the 272,273 engines don't jump time as a rule, usually those engines have intake manifolds that come apart internally and the engine swallow intake parts or plastic parts , which result in bent valves, and coils bad are common, check compression first!