An engine firing order is the specific sequence of ignition for each cylinder in an internal combustion engine containing multiple cylinders. Firing orders, which are typically nonsequential, are designed to reduce engine vibration and are specific to an individual model of engine.
The firing order is an important part of the overall design of the engine and is determined during the design of the engine to eliminate as much engine vibration as possible. If the firing order is changed or adjusted, the ignition from the spark plug is delivered at the wrong time and the engine functions poorly or does not run. The firing order for a particular engine is typically found in the repair manual specific to that model.