Firing order

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The firing order of an internal combustion engine is the sequence of ignition for the cylinders.

In a spark ignition (e.g. gasoline/petrol) engine, the firing order corresponds to the order in which the spark plugs are operated. In a diesel engine, the firing order corresponds to the order in which fuel is injected into each cylinder. Four-stroke engines must also time the valve openings relative to the firing order, as the valves do not open and close on every stroke.

Firing order affects the vibration, sound and evenness of power output from the engine and heavily influences crankshaft design.