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My 2012 CLS 63 just started having serious misfire issue yesterday. When the engine is cold it runs great with no codes. As soon as it gets to operating temperature it starts throwing misfire codes on cylinder 1 and 4 and runs rough. If I continue to drive it I get misfires progress to cylinders 5 and 8 and barely runs. It seems like fuel is dumping into the cylinders at least on bank 1.
I checked live data and noticed while idling it had a long term fuel trim on bank 1 of over 80% and bank 2 was 15%. Fuel rail pressure was 11510 kPa. I will capture more live data when it's cold to see how things change as it warms up.
I'm not sure if the misfires are contributing to the high fuel trim or the excessive fuel is causing the misfires.
The car is undriveable now. Anyone else have an experience like this. The car has 107k miles on it and has run perfectly for me over the 40k miles I've owned it. This came out of nowhere.
Time for coils and plugs if not changed yet, check the stickies on w212.
Bosch plugs were recently installed and a few boots replaced that were damaged. Would 1 or 2 bad coils escalate to misfires across all cylinders. It’s strange that it runs great until it warms up. The other strange thing is I swapped coils around but the misfires stayed on 1 and 4
compression test?
ok i saw now your post in w212, i would say also that the issue is in fuel pressure cause misfires on many cylinders not only 1 and 4 but only if lean afr, if it dump lot of fuel i suspect front oxygen sensors.
Last edited by Robert AMG; Jun 2, 2025 at 06:12 PM.
I pulled the fuel rail with injectors and got consistent ohm reading on all 4. I’m struggling to pull an injector out of the rail. I removed the retainer clip and the injector rotates but I couldn’t pull it out. I’m concerned about damaging the injector.
scoped each cylinder through the injector holes. No surpise, 2/3 are dry and 1/4 are wet. Walls look good and I see no evidence of contact between valves and piston.
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