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Q: Engine occasionally misfires

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Engine occasionally misfires...typically when down shifting or driving up hill. Had engine light on and code was for O2 sensor (bank 1 sensor 1) Took to dealership and they replaced transfer case. They apparently didn't see issue with O2 sensor so they did not mess with it. Still had the same issues and occasional engine light so I replaced all spark plugs and two O2 sensors...now just had engine light come on throwing code for catalytic converter. Any thoughts of if the issues are connected or maybe something went wrong when replacing spark plugs and sensors? Really don't want to spend $1000 on replacing converter.

My car has 170000 miles.
My car has an automatic transmission.

Hi there, thanks for writing in. In most cases, if you have an error code show up, make the change of components and don’t reset to the error code with a digital scanner, the issue will still continue. This is very common with O2 sensors. However, the misfiring issue may be contributed to an ignition system problem, such as a crankshaft sensor or camshaft sensor.

The best thing you can do is contact a local professional mechanic and have them complete a misfire inspection to avoid any unnecessary repairs. This should allow them to pinpoint the precise problem so you don’t have to spend $1000 on replacing a part that is most likely not the source of your problem.

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