The failure of the fuel charge in one or more engine cylinders to fire or ignite at the proper time. It can be due to poor compression caused by worn or improperly adjusted valves, worn piston rings , a faulty head gasket , or in the case of a two-stroke engine leaking crank seals. It can also be caused by poor ignition due to worn or dirty spark plug electrodes , worn or improperly gapped points or spark plugs, poor fuel delivery, faulty ignition wiring, or faulty distributor components . An easy way to detect the problem is to put a stiff piece of paper at the end of the tail pipe and listening for an irregular puffing sound. Also called "missing".