Misfires are probably one of the more common engine problems. They can be caused by a variety of problems, often something to do with the spark plug. Usually an engine can run okay with a minor misfire, but if it’s bad enough, it can actually lead to catalytic converter failure, which is an expensive repair. Usually the check engine light will flash if there’s a misfire this bad.

This Honda Odyssey came into the shop with a very bad misfire. You can usually hear a bad misfire in the sound of the engine or feel a vibration, but this was even easier to hear than most. One of the spark plugs had actually melted and come loose from the cylinder head. When there’s an open hole into a cylinder of a running engine, it’s very loud.

Not surprisingly, not only did the spark plug melt, but so did the ignition coil. A non-melted coil is on the right. I don’t know what was causing such a bad misfire, but melting a spark plug is impressive. I’ve seen a plug or two pull out the threads and blow out of the hole before, but they weren’t melted like this. As you might expect with the plug melted like this, the cylinder head was also destroyed, so the engine would need at least a cylinder head.

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-Dan