Q: If cylinder 3 misfires is that a bad thing?

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I brought this car to get a diagnostic test. It stated that cylinder 3 misfired and that the catalyst is damaging. Is this bad and expensive?
My car has an automatic transmission.

Hi there. A misfiring cylinder can be expensive if allowed to continue. The catalytic converter can be damaged. If the cylinder is misfiring, the coil, wire, and/or spark plug could be the cause. First swap the spark plug between cylinder 3 and one of the other cylinders. Make sure to note which ones you swapped. Check to see if the misfire moves from cylinder 3 to the other cylinder. If this is the case, then replace the spark plugs as the swapped plug is at fault.

If there is no change, then the wire or coil may be at fault. Wire and coil resistance can be checked with a digital volt/ohm meter and compared to specifications. If you would like to have a professional take a look, a certified technician from YourMechanic can come to your car’s location to diagnose the misfire and follow through with appropriate repairs.

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