Fuel Injection System - 3.3L/3.8L PFI: Description: Notes

The Port Fuel Injection (PFI) system is controlled by the Electronic Control Module (ECM). The ECM monitors engine operation and environmental conditions. In addition to other functions, ECM output signals provide correctional adjustments for air/fuel mixture and idle speed.

Standard PFI systems feature simultaneous double-fire injection. Fuel injectors are pulsed once for each engine revolution, each spray providing 1/2 the fuel required for the combustion process.

The 3.8L models use Sequential Fuel Injection (SFI). Injectors on these models pulse sequentially in spark plug firing order. Main differences between these systems are injectors, wiring and the ECM.

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

NOTE: Primary sub-systems affecting fuel system operation are covered in this article. Because of interrelated computer functions of system, refer to appropriate article in COMPUTERIZED ENGINE CONTROLS section for information on other ECM systems.