2001 Mercedes Benz CL55 AMG Multiple misfires on cylinders #5,#6,#7,and #8 5.5L

I am experiencing multiple ms-fires on the drivers side engine cylinders. #5,#6, #7, and #8. I suspect I have a plugged or restricted exhaust on the one side. It runs fine when I start it. It doesn't throw the check engine until I put it in gear and try and drive it down the road. I have changed all 16 spark plugs. I moved one of the coils to the passenger side companion cylinder and still have the same D.T.C. codes, which leads me to believe it is the exhaust causing my issue with the engine. If it can't exhale, it won't inhale and cause the misfires. What should I do to prove my theory? Who to take it to, to resolve my issue?

Does the engine feel like it's missing on four cylinders? With those codes, there should be at least some noticeable loss in power during acceleration. If you feel a miss, lets continue testing. If you don't, then you're possibly seeing 'false' misfires.

The most straightforward way to confirm a plugged cat would be a backpressure test at the drivers side O2 sensor port. Backpressure gauges are fairly cheap, or can be rented from a parts store. The problem will be getting to the O2 to remove it! You'll have to be the judge on if doing this is worth your time or not. :silly:



Before that, it'd be a good idea to have a look at scan data. Typically, when one converter plugs, the fuel trims get severely skewed. One side will go lean (positive numbers) and the other will go rich (negative numbers). This is a classic indication of a breathing issue. No special Mercedes scanner would be required - a parts store Global OBD model with scan data capabilities would work.

If the drivers side bank is truly not breathing correctly, it'll have the negative fuel trims during acceleration. The problem with this method is that the engine computer may go into open loop once the misfire is detected, and stop using fuel trims. Again, this is something you have to observe for yourself.

Thank you for the response. It is noticeable when driving the car especially when accelerating up an inclined road. Once I have proven the exhaust is restricted, I am guessing I will need to go to a muffler shop to get the catalytic converter replaced on the driver side and clear the engine code from the computer. I bought the car from a car auction so i inherited this issue.

Thanks for getting back to me. Definitely not a false misfire, then.

Let me know what you find with those tests, and we can go further if needed. You may not need a muffler shop, necessarily, just one willing to get their hands dirty on an AMG. :lol: Someone with Euro experience would be preferable. Parts availability would be another question.