Fuel Injection System - PFI: Description: Notes

All General Motors models with Port Fuel Injection (PFI) systems have fuel delivery controlled by an on-board computer, the electronic control module (ECM). The ECM monitors engine operations and environmental conditions. It generates output signals to provide the correct air/fuel mixture, ignition timing and engine idle speed.

Standard PFI systems feature simultaneous double-fire injection. On these systems, all injectors pulse once each engine revolution. Thus, 2 injections of fuel are mixed with incoming air to produce the charge for each combustion cycle. On Buick Riviera and Buick Regal, the injectors are pulsed sequentially (1-by-1) in spark plug firing order. This system is referred to as Sequential Fuel Injection (SFI). Camaro and Corvette PFI system is referred to as Tuned Port Injection (TPI).

All 3 systems maintain constant fuel pressure to the injectors. Therefore, air/fuel ratio is adjusted by varying injector pulse width ("on" time). The ECM processes information from various sensors to compute the pulse width. There are 2 major sub-systems; the fuel system and the electronic control system. The mechanical portion of the port fuel injection system consists of fuel injectors, throttle body, fuel rail, fuel pressure regulator, idle air control (IAC) valve, fuel pump and fuel pump relay.

NOTE: Primary sub-systems affecting fuel system operation are covered in this article. Because of interrelated functions of Computer Command Control (CCC) system, refer to GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROLS section for more information.