Q: Car's #8 cylinder is misfiring

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There is a misfire in my car’s #8 cylinder. Even after changing the spark plugs and the ignition coil, I still have the misfire. When checking the compression in the cylinder, I found that it is good. Also, I checked to ensure that there is 12v going to the injector - that is fine, too. There is a code for the catalytic converter. Could the catalytic converter be causing the misfiring and if not, what do I look for next?

A: It is possible that your oil ring could be ...

It is possible that your oil ring could be faulty in the number eight cylinder. If the oil ring is faulty, this can allow oil to get past the piston into the combustion chamber and therefore causing it to get burned by the spark plug. This can cause a misfire because oil is much harder to burn than gasoline.

Extended burning of oil by a spark plug can eventually foul out the spark plug. If the oil ring is the only piston ring that is bad, this can still cause the compression readings to be within specification. I would recommend having your number eight cylinder checked by a professional to determine if there is evidence of oil in the combustion chamber. If there is evidence of oil, I would recommend having the oil ring replaced.

Have the vehicle inspected by a qualified mechanic, they will be able to diagnose the misfire firsthand and make the appropriate repairs.

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