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Discussion Starter #1 (Edited)
I bought a 2006 S500....either for myself or my attorney...we have bounced back and forth on who should keep this beauty. He was driving on the freeway a few weeks ago and hit passing gear and tripped the Check Engine light, and the car ran rough. I scanned the codes and found misfire on cylinder #8. The car was running rough...I thought maybe it was a misfire due to a weak coil, so I switched the #5 and #8 coils and erased the codes. After several hundred miles, there was no problem.

This morning I got a good backache replacing the 16 spark plugs...we then took the 500 to a car wash and powerwashed the engine. After leaving the car wash, my attorney then hot rodded the S500...hit passing gear...I think two downshifts, and then the check engine light tripped again. Meanwhile I lost my scanner so we went to Autozone. They scanned the codes and found misfire on cylinder #8 again....so my conclusion is that it is not the coil nor the plugs. The Autozone guy spilled some BS that maybe there was some carbon buildup on the #8 piston that is now coming in contact with the spark plug and reducing the gap, then tripping a code. I don't buy it.

My guess is that it is a faulty fuel injector. FYI, after the code is erased, the 500 runs great...so I feel that the fuel injector is somewhat restricted, and at high RPMs, it trips the code, which then ends up shutting off the fuel delivery to cylinder #8.

Any opinions are appreciated.
 

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2004 W220 (S430) ; 2001 R129 (SL500) Sport
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Run some Techron through the fuel system and hit "scoot" again. It's the only fuel additive MB accepts, and it's pretty good stuff. I use it in a higher concentration than the dose recommended, and I can't swear there is any difference because the car wasn't acting up to begin with, but it's the only thing I can think to do without pulling the injector and cleaning it. If the Techron doesn't work, you're just out a few bucks for the additive and no harm done. If it does, you've saved a lot of work you didn't need to do.
 

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ml500 w163 2002
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456 Posts
I bought a 2006 S500....either for myself or my attorney...we have bounced back and forth on who should keep this beauty. He was driving on the freeway a few weeks ago and hit passing gear and tripped the Check Engine light, and the car ran rough. I scanned the codes and found misfire on cylinder #8. The car was running rough...I thought maybe it was a misfire due to a weak coil, so I switched the #5 and #8 coils and erased the codes. After several hundred miles, there was no problem.

This morning I got a good backache replacing the 16 spark plugs...we then took the 500 to a car wash and powerwashed the engine. After leaving the car wash, my attorney then hot rodded the S500...hit passing gear...I think two downshifts, and then the check engine light tripped again. Meanwhile I lost my scanner so we went to Autozone. They scanned the codes and found misfire on cylinder #8 again....so my conclusion is that it is not the coil nor the plugs. The Autozone guy spilled some BS that maybe there was some carbon buildup on the #8 piston that is now coming in contact with the spark plug and reducing the gap, then tripping a code. I don't buy it.

My guess is that it is a faulty fuel injector. FYI, after the code is erased, the 500 runs great...so I feel that the fuel injector is somewhat restricted, and at high RPMs, it trips the code, which then ends up shutting off the fuel delivery to cylinder #8.

Any opinions are appreciated.
i have the same problem with my 55 motor. It only happens when I hotrod the car on the highway at High RPMs past 5700 and I'm pushing it hard. #8 cylinder also. Do you have any idea what caused this? did techron help you?
 

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Since we're brainstorming, what about swapping the injector to another cylinder? What about the plug wires as well?

Still strange another car does it on the same cyl. Wondering if the rev limiter is shutting down cyl 8 first and it stays off until reset??
 

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Discussion Starter #5
I ran the techron and didn't have the problem for months until last week - same exact thing....I ordered a new injector today and will report back....
 

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I ran the techron and didn't have the problem for months until last week - same exact thing....I ordered a new injector today and will report back....
Did the techron work? I have the same problem with my car. changed plugs, etc. when hot rotted, check engine light turns on with random misfire.
 

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Most likely the problem is related to the spark plug cable because if you swapped the ignition coils the problem carried over. I suggest to buy OEM Bosch spark plug wires only, I have seen this happen to some Mercedes-Benz and the spark plug wire was the culprit.
 
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