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Engine misfire cylinder 6 only at high rpm?

25K views 35 replies 9 participants last post by  megadamp 
#1 ·
This is my first Mercedes I bought used in Jan 2008 a 2002 ML320 with 56,000 miles it was a great deal and looked almost new.

Now My ML320 has 72,000 miles recently starting having a problem during acceleration like on the freeway or uphill. When I press the gas to downshift the CEL would come on and the engine would run rough until I turned it off then runs fine. After several starts/stop CEL is off and it continues to run fine, until next time I try to accelerate fast.

I took the car to an independent mechanic and at first they said replace all the plugs and wires plus they saw a misfire on cylinder 6 replaced the #6 coil as well. OK, problem still there, upgraded/recalibrated the ECU, problem still there.

The mechanic now say that there is a floating valve on #6 at around 5000 rpm
that is causing the misfire and the ECU is turning off the #6 injector and turning on the CEL. He states that as long as I drive less aggressively it should be fine and the bad valve won't be a problem.

I respect this mechanic and I think he honestly believes what he is telling me.
However, my gut feeling is that this is a different problem, possibly MAF which he said there is no code for this in the log and if it was the MAF it would misfire on more than one cylinder. He says this is only misfiring on #6 no other. Unfortunately I don't have the codes.

I really like this car however if it is going to be a continuing problem, then it is back to the Japanese cars for me, where I have had better experience.

Any ideas or opinions are welcome and appreciated.
 
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#33 ·
I am sure how to take that last post, since I am the OP I guess it was a response to my last post.

I NEVER said I believe it was a valve problem?? In fact I never believed it was a valve problem. If I had believe this was a valve problem I would have never started this thread.

If you had read my last post I stated that I have not experienced this problem for several years, after some basic repair work was done. Why should I fix something that isn't broken any longer. My ML320 has been running perfectly for about 4 years!

I don't have the tools or the time to try to swap the O2 sensor and whatever else that might have been suggested. I would have to hire a mechanic to do these things so how does that save me any money?

I appreciate everybody's help and suggestions, other than the one from megadamp which was nothing more than a "put down" because he didn't read my post. I also noticed that megadamp never offered any real suggestions, but I guess there is always one like this in any group.

I will think twice about posting on this forum in the future.
 
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