Firing order

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, to improve engine balance and achieving smooth running, for long engine fatigue life and user comfort, and heavily influences crankshaft design.

In a gasoline engine, the correct firing order is obtained by the correct placement of the spark plug wires on the distributor. In a modern engine with a direct ignition and the Engine Control Unit(ECU) or Engine Management system takes care of the correct firing sequence. Especially on cars with distributors, the firing order is usually cast on the engine somewhere, most often on the cylinder head, the intake manifold or the valve cover(s).

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

Mercedes-Benz M272 engine, Volkswagen V6's (both engines are 90-degree V6's)
GM 3800 engine, Rover KV6 engine
General Motors 60° V6 engine, Mazda JE 3.0 litre 60-degree V6 engine, Chrysler Pentastar engine,
Ford Cologne V6 engine, Ford Essex V6 engine (UK)
Chevrolet Corvair
Subaru Alcyone/XT-6/Vortex ER-27 Flat-6
Porsche Boxster Flat-6
Maserati Quattroporte IV V6-4AC-24
Toyota HZ engine

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Wikipedia