Mechanical Returnless Fuel System
WARNING: This page is about a different variant/trim than selected.
NOTE:
Fuel rail pulse damper used on mechanical returnless fuel systems should not be confused with a fuel pressure regulator. Both are visually similar, but the fuel rail pulse damper does not regulate fuel pressure. Damper is used to reduce fuel system noise. Vacuum port on fuel rail pulse damper is connected to manifold vacuum to avoid fuel spillage if damper diaphragm ruptures.
Electronic returnless fuel system consists of a fuel tank with reservoir, fuel pump, fuel pressure regulator, fuel filter, fuel supply line, fuel rail, fuel rail pulse damper, fuel injectors, and Schrader/pressure test port. The following list of components and their specific operation corresponds to numbers in illustration. See Fig 1.
- The fuel delivery system is enabled during crank or running mode once PCM receives a Crankshaft Position (CKP) sensor signal.
- The fuel pump logic is defined in the fuel system control strategy and is executed by PCM.
- The PCM grounds fuel pump relay, which provides Vehicle Power (VPWR) to fuel pump.
- The Inertia Fuel Shutoff (IFS) switch is used to de-energize fuel delivery secondary circuit in the event of a collision. IFS switch is a safety device that should only be reset after a thorough inspection of the vehicle (following a collision). For additional IFS information, see INERTIA FUEL SHUTOFF SWITCH (ALL FUEL SYSTEMS) .
- A pressure test point valve (Schrader valve) is located on fuel rail. This is used to measure fuel injector supply pressure for service and diagnostic procedures. On vehicles not equipped with a Schrader valve, use Rotunda Fuel Pressure Test Kit (134-R0087) or equivalent.
- The fuel rail pulse damper is located on fuel rail to reduce fuel system noise caused by pulsing of fuel injectors. The vacuum port located on damper is connected to manifold vacuum to avoid fuel spillage in the event pulse damper diaphragm were to rupture. Pulse damper should not be confused with a fuel pressure regulator.
- The fuel injector is a solenoid-operated valve that meters fuel flow to each cylinder. Fuel injector is opened and closed a constant number of times per crankshaft revolution. Amount of fuel is controlled by length of time fuel injector is held open. Fuel injector is normally closed and is operated by a 12-volt VPWR signal from power relay. The ground signal is controlled by PCM. For additional fuel injector information, see FUEL INJECTORS under FUEL CONTROL.
- There are 3 filtering or screening devices in fuel delivery system. The intake sock is a fine, nylon mesh screen mounted on intake side of fuel pump. See Fig 2. There is a fuel filter screen located at fuel rail side of fuel injector, and the fuel filter assembly is located between fuel pump and pressure test point/Schrader valve.
- The Fuel Pump (FP) module contains fuel pump, fuel pressure regulator and fuel sender assembly. The fuel pump has a discharge check valve to maintain system pressure during shutdowns and to minimize starting problems. Fuel pressure regulator is attached to fuel pump in fuel pump module located in fuel tank. It regulates fuel pressure supplied to fuel injectors. The fuel pressure regulator is a diaphragm operated relief valve, wherein fuel pressure is established by a spring preload applied to diaphragm. Excess fuel is by-passed through regulator and returned to fuel tank.
Courtesy of FORD MOTOR CO.