Fuel Injection Systems

Diagram of a multiport fuel injection system.

Multiport and sequential fuel injection systems both inject atomized fuel into a port just before the intake valve. There is a difference in the way these systems operate. Multiport injection systems fire the injectors in groups. A four-cylinder engine may fire the #1 and the #3 injectors on the first crankshaft revolution and then fire the #2 and #4 on the second revolution. A six-cylinder engine would fire groups of three injectors on the first revolution and then fire the other three on the next revolution. The fuel charge in some cylinders momentarily sits, but engines rotate so quickly the delay is negligible. Due to its design, a problem with one driver will cause a misfire in more than one cylinder.

Diagram of a sequential fuel injection system.

Sequential fuel injection systems fire each injector individually. This system is more efficient than a multiport system because changes to the fuel mixture are instantaneous. Sequential fuel injection systems are installed on most of today's engines. The PCM controls the injectors by pulse width, the length of time the injector sprays fuel into the port. Pulse width control of each injector improves performance over multiport injection.