Fuel Delivery and Air Induction: Description and Operation

Fuel System:

The Fuel System consists of three major subsystems; a fuel storage system, fuel injectors with the supporting fuel injection control system, and a fuel delivery and return system.

FUEL STORAGE
The fuel storage system consists of a fuel tank, fill spout and filler cap. The filler caps primary function is as an evaporative emissions control device and is therefore covered in detail in EMISSION CONTROLS. The remaining components are covered in this section by name.

FUEL INJECTION AND CONTROL
The Injectors are solenoid operated shutoff valves designed to deliver fuel in an appropriate spray pattern to promote total fuel atomization in the intake air stream
The Fuel Injection Control System consists of the ECU (Electronic Control Unit) and all of the engine and operating condition sensors. Using the information from the sensors to determine the proper fuel amount and delivery time, the ECU varies the injectors "ON" time to adjust the amount of fuel delivered during each individual firing cycle. The ECU also controls the MODE of operation. In normal operating MODE, the ECU activates the injectors in a sequential order, synchronous to the firing order. In cold start MODE, the ECU commands the injectors to operate in a non-synchronous pattern (simultaneously activates all injectors on each cylinder pulse) to enrich the air/fuel ratio and promote cold condition vaporization. In acceleration MODE, an additional injection of fuel is provided for the first two cylinders immediately following the ECU sensing an acceleration condition. The additional injection pulses continue as long as the ECU senses an increasing acceleration condition.
For a more detailed description of the fuel injection system operation, refer to COMPUTERIZED ENGINE CONTROLS. For all Fuel System mechanical component descriptions, refer to this section by component name.

FUEL DELIVERY AND RETURN
The fuel delivery components consist of fuel supply lines, a high pressure fuel pump (mounted in the fuel tank), a fuel filter assembly, a fuel pressure accumulator and a fuel pressure regulator. The delivery systems function is to deliver fuel at a pressure and quantity high enough to allow the fuel regulator to maintain a constant fuel pressure in the fuel delivery rail (in reference to the intake manifold pressure) under all driving conditions. Additionally a check valve in the fuel pump holds pressure against the system for a period of time after engine shutdown to ensure adequate pressure is available during warm engine re-start conditions.
The Fuel return portion of the fuel system consist of lines and couplings and therefore is addressed, jointly with the fuel supply lines, under the heading of FUEL/VAPOR LINES. The function of the return line is to recover excess fuel vented by the fuel pressure regulator (mounted on the fuel rail) and return it to the fuel tank. The fuel return line is low pressure and returns directly to the fuel tank.
The Vapor recovery system also consists of lines and couplings addressed under the heading of FUEL/VAPOR LINES in this section. The function of the vapor lines are to provide a route for the recovery of fuel vapors (from the fuel tank) either for storage in the charcoal canister, or for evacuation through the purge control system. Additionally contained in the vapor recovery system are two components, an overfill limiter and a fuel check valve. These components primary functions are as evaporative emissions control devices and are therefore covered in detail in EMISSION CONTROLS.