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Q: Cylinders 4 and 5 are misfiring - 2007 Mercedes-Benz S55 AMG

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In my vehicle, there is a problem that I’m having where there is a misfire on cylinder 4 and 5. I changed the coil packs, but the same misfire is still happening. The problem might be the ECU that sits on the engine. If you need the part number, it is: A2731535079. In your expertise, please tell me what I need to do to fix my car’s problem.

A: Hello. Most of the time if there is a misfi...

Hello. Most of the time if there is a misfire on those two cylinders it is not caused by the computer. Typically it is caused by either failing spark plugs or an internal problem. I usually start by doing a compression test of the engine. If the pressure is low in either of those cylinders then this will occur. If the compression is fine then the spark plug and coils need to be inspected even though they are new. If those are also fine, then the circuit will need to be tested to see if they are getting a good signal. It is common to have a bad connection at the coils which will cause this to occur. If you are going to have this repaired, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose the misfiring problem and proceed with correct repairs.

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