Fuel Injection Systems

Diagram of a multiport fuel injection system.

Multiport and sequential fuel injection systems inject atomized fuel into a port just before the intake valve. There is a difference in the way these injectors are fired though. Multiport injection systems fire the injectors in groups. A four cylinder engine may fire the #1 and the #3 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 is more efficient because changes to the fuel mixture are instantaneous. Sequential fuel systems are found on most of today’s engines. These injectors are also ground controlled by the PCM. The pulse width or on time of each injector is more precisely timed for improved performance over multiport injection.