Q: Would bad spark plugs cause misfire in cylinder?

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I have never replaced my spark plugs (30k miles) and they are the wrong brand plugs. My engine is misfiring in cylinder 5 and the cylinder is filling up with fuel and igniting causing flames to shoot out a hole in my exhaust pipe when I was checking back pressure. Could this be a cracked head or bad spark plug?

My car has 139200 miles.
My car has an automatic transmission.

A misfire could be caused by a bad spark plug. It could also be caused by a bad coil, fuel injector, an air leak, a compression problem, or a camshaft problem, or yes, even a bad head gasket or a cracked cylinder head. So it is way too soon to assume the worst. If you’ve never changed your spark plugs, that is a good place to start because it’s time anyway. But I wouldn’t spend money on any other parts until you get a proper diagnosis. You can have that done at your convenience by contacting YourMechanic. They can send a technician to your home or office to check out your Misfiring problem and let you know what is the solution.

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