Fuel Injection System - Multi-Port: Description: Notes

The Port Fuel Injection (PFI) system is controlled by an on-board computer known as the Electronic Control Module (ECM). The ECM monitors engine operations and environmental conditions. The ECM output signals provide correct air/fuel ratio, ignition timing and idle speed.

Standard PFI systems feature simultaneous double-fire injection. Fuel rail, mounted to the intake manifold, provides fuel for the injectors. Fuel is constantly circulated through the rail during engine operation.

Injectors pulse once for each engine revolution, providing fuel directly to combustion chamber with precise timing. On Sequential Fuel Injection (SFI) models, injectors pulse sequentially in spark plug firing order. Differences between these systems are injector wiring and the ECM.

In all systems, constant fuel pressure is maintained to the injectors. Air/fuel ratio is adjusted by the time that injector stays open (pulse width). Various sensors provide information to the ECM to control pulse width. There are 2 major sub-systems; fuel system and electronic control system.

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 COMPUTER CONTROLS section for additional information.