I touched a little on misfires in the spark plug part of this article, but I’d like to cover them in more detail here. Misfires come in all shapes and sizes. They have an equal amount of causes. In this section, and some of the sections following it, I’ll talk about the possible causes of engine misfires. The bottom line is, misfires cause performance problems as well as poor fuel economy. A misfire occurs when a cylinder or cylinders don’t put out the power that they should. Misfires make the engine work harder, making it less efficient.