Missfire is the failure of the fuel/air mixture in one or more cylinders to undergo combustion while the car is running. Misfiring can be due to poor compression caused by worn or improperly adjusted valves, worn piston rings, or a faulty head gasket. Or it can be caused by poor ignition due to worn or dirty spark plug electrodes, worn or improperly gapped spark plugs, poor fuel delivery, faulty ignition wiring, or faulty distributor components.