Fuel Delivery and Air Induction: Description and Operation

The Fuel System consists of three major subsystems; the fuel storage system, the fuel injector and 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 cap seals the fuel tank, and provides for pressure release and vacuum release. The fill spout contains a restrictor to prevent the addition of leaded fuels to the fuel tank. The fuel tank is a closed unit, utilizing a vapor control system to prevent fuel vapors escaping to the atmosphere.

FUEL INJECTION AND CONTROL
The Injectors are solenoid operated valves, designed to deliver fuel in a conical spray pattern to promote total fuel atomization in the intake air stream.
The Fuel injection control system consists of the Electronic Control Unit (ECU) and all of the engine operating condition sensors and switches. Using the information from the sensors and switches to determine the proper amount and timing of fuel delivery, the ECU varies injector "ON" time, or "pulse width", 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.

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 system, delivers fuel at a pressure and quantity high enough to allow the fuel regulator to maintain a constant fuel pressure in the fuel delivery pipe (in reference to the intake manifold pressure) under all driving conditions. Additionally a check valve in the fuel pump maintains pressure in the system for a period of time after engine shutdown, to ensure adequate pressure is available during engine re-start conditions.
The Fuel return portion of the fuel system returns excess fuel vented by the fuel pressure regulator (mounted on the fuel delivery pipe) to the fuel tank. The fuel return line is under low pressure.
The Vapor recovery system, recovers 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.