Returnable Fuel System
The returnable fuel system consists of a fuel tank with a reservoir, the fuel pump module, the fuel supply lines, the fuel filter(s), a Schrader valve/pressure test point, the fuel rail, the fuel injectors, and the fuel pressure regulator. Operation of the system is as follows
Scheme 74
- The fuel delivery system uses the crankshaft position (CKP) sensor to signal the PCM that the engine is either cranking or running.
- The fuel pump logic is defined in the Fuel System control strategy and is executed in the PCM. The PCM grounds the fuel pump relay for one second during key on and engine off. During crank the fuel pump relay is grounded as long as the PCM receives a CKP signal.
- The fuel pump relay has a primary and a secondary circuit. The primary side is controlled by the PCM and the secondary side provides B+ to the fuel pump circuit when the relay is energized.
- The inertia fuel shut-off (IFS) switch is used to de-energize the fuel delivery secondary circuit in the event of a collision. The IFS switch is a safety device that should only be reset after a thorough inspection of the vehicle following a collision.
- The fuel injector is a solenoid-operated valve that meters fuel flow to each combustion cylinder. The fuel injector is opened and closed a constant number of times per crankshaft revolution. The amount of fuel is controlled by length of time the fuel injector is held open. The injector is normally closed and is operated by 12-volt VPWR from the power relay. The ground signal is controlled by the PCM.
- A pressure test point valve (Schrader valve) is located on the fuel rail. This is used to measure the fuel injector supply pressure for repair and diagnostic procedures. On vehicles not equipped with a Schrader valve, use the Rotunda Fuel Pressure Test Kit #134-R0087 or equivalent.
- The fuel pressure regulator, also referred to as the pulse damper, is mounted to the fuel pump bracket within the fuel tank. It regulates fuel pressure supplied to fuel injectors. (Scheme 74)Balancing one side of the diaphragm with manifold vacuum maintains a constant fuel pressure drop across the fuel injectors. Fuel pressure is high when engine vacuum is low. Excess fuel is bypassed through the fuel pressure regulator and returned through the fuel return line to the fuel tank.
- There are 4 filtering or screening devices in the fuel delivery system. The fuel intake sock or screen is a fine, nylon mesh mounted on the intake side of the fuel pump. There is a fuel filter screen located at the fuel rail side of the fuel injector. A fuel filter/screen is located in the inlet side of the fuel pressure regulator. The fuel filter assembly is located between the fuel pump and the pressure test point/Schrader valve.
- The fuel pump (FP) module is a device that contains both the fuel pump and the fuel sender assembly. The fuel pump is located inside the reservoir and supplies fuel through the fuel pump module manifold to the engine and the fuel pump module jet pump.
Note. Some vehicles have the relay located in the battery junction box.
