What is the firing order of an engine?

The firing order is the sequence of power delivery of each cylinder in a multi-cylinder reciprocating engine.

This is achieved by sparking of the spark plugs in a gasoline engine in the correct order, or by the sequence of fuel injection in a Diesel engine.

When designing an engine, choosing an appropriate firing order is critical to minimizing vibration and achieving smooth running, for long engine fatigue life and user comfort, and heavily influences crankshaft design.

In case of 4 cylinder engine: the four crankpins are in one plane, 180o opposed. Since two pistons each are at the extreme position, the inline design permits following firing orders: 1-3-2-4 or 1-3-4-2

1-3-2-4

1-3-4-2

In case of 6 cylinder engine: the crankpins are in one plane, 120o apart. The inline design permits following firing orders: 1-5-3-6-2-4 or 1-4-2-6-3-5

1-5-3-6-2-4 or 1-4-2-6-3-5