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I’d like to reach out to you about a technical issue I’m experiencing with my car, and I’m hoping for some advice or recommendations. The car is a Mercedes W203 C320 with the M112 engine. The problem occurs under full load and at over 5000 RPM – cylinder 6 shuts off, and the Check Engine light comes on. After restarting the engine, the cylinder resumes normal operation, but the light remains on. However, if I exceed 5000 RPM again, the issue repeats. Interestingly, this happens about 4 out of 5 times.
Xentry only shows errors for "misfire cylinder 6" and "misfire detected" (codes P306 and P300). Here’s what I’ve tried so far to resolve the issue:
New spark plugs, swapping the coil and wires with another cylinder – still records cylinder 6.
Checking the front lambda sensors; there are no error codes, but I still put the old ones back, which occasionally showed mixture adaptation (from what I recall), but the car didn’t go into limp mode – no change, as cylinder 6 still shuts off after 5000 RPM.
The car has no catalytic converters, and the secondary lambda sensors are disabled.
Compression test – this part was interesting because all cylinders showed around 12 atmospheres, give or take 0.1, whereas the specification says it should be 10. The tool I used (a GEKO) might not be fully accurate, or there might be a bit of oil leakage from the valves, causing air to blow into the rings. However, the fact that they’re all consistent with each other is reassuring.
I checked all vacuum hoses – no leaks anywhere, the swirl flap valve is intact and operational, as are the additional air valves.
The MAF sensor shows adequate values except for the intake air temperature (which has been showing an error ever since I installed an NGK airflow meter).
I don’t think the fuel injectors are responsible for this specific issue because the car has an LPG system, and the problem occurs on both fuels.
If anyone has had a similar issue or has ideas on what else I could check, I would greatly appreciate any advice or suggestions. I’m running out of ideas and would be grateful for any guidance or input that could help.
Thanks in advance to everyone who takes the time to help!
Too funny I got a cyl 6 misfire 2 days ago, I guess I'm following this thread too!
So far I swapped the 5 and 6 coils to see if it follows, nothing yet...
Too funny I got a cyl 6 misfire 2 days ago, I guess I'm following this thread too!
So far I swapped the 5 and 6 coils to see if it follows, nothing yet...
I actually have a cylinder 1 and 6 misfire. tried swapping coils, spark plugs, etc. but nothing seems to solve it. it only happens when i step far down on the pedal, not necessarily WOT, but when i force the engine it cuts cylinder one and six. i have a diffuser on my exhaust and it sounds like a modern car changing gears (lol). i think in my case it is caused by a electrical problem. i checked and 12v arrives at the coil even when the cylinder cuts, but the car has a few electrical bugs that happens sometimes (window stops working out of nowhere sometimes and comes back to life when i unplug the battery for a minute and plug it back in). in the case of the engine, i only need to stop the car, shut down the engine and start it up again and the misfire goes away. oh, one more thing, when the misfire is happening, the engine does not change when i unplug the cylinder 6 coil, so its out for good. but it changes a little bit when i unplug cylinder 1 coil, so maybe just 1 spark plug is out? hmm i dont know. i'm new to this mercedes world... i just bought the car a few weeks ago. i hope i can find someone with the solution. i have read so many forum pages about similar problems, i have posted so many threads too, but nothing yet. sadly there is no shop in my town who works with this kind of car, so i'm on my own here
Did you find any solutions? I have a similar problem (w211 e320 m112.949) I suspect a clogged catalytic converter I changed the spark plugs and wires and coils
i haven't found a solution yet. i redone all welding points + chemical bath on both ECU and SAM. Nothing changed. I still have to unplug the battery quite often... but i'm still working on it. In my case i think it is related to a electrical problem, but if you dont have another problems, just the misfire, it can be a O2 sensor or a clogged catalytic converter! you can check this with a cheap bluetooth scanner + a adapter
i haven't found a solution yet. i redone all welding points + chemical bath on both ECU and SAM. Nothing changed. I still have to unplug the battery quite often... but i'm still working on it. In my case i think it is related to a electrical problem, but if you dont have another problems, just the misfire, it can be a O2 sensor or a clogged catalytic converter! you can check this with a cheap bluetooth scanner + a adapter
i have cylinder 1 4 5 misfire and p0300 multiple misfire p0403 egr code fault, bought new catalytic converter changed 1x o2 sensor.
didnt find what is the problem, im confused
if i drive normal, car dont give any misfire fault but over 4-5k rpm start again
Last edited by Mb3205835; Sep 27, 2025 at 05:13 AM.
Hello group, I apologize for the late reply, but better late than never. The problem with me turned out to be the camshaft sensor, apparently at high revs it does not measure correctly and the easiest way for it to turn off a cylinder, I replaced it with a Bosch one, but the problem remained, then I tried Febi and it solved the problem. I hope I can still help someone with this topic.
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