Mechanical Returnless Fuel System (MRFS)
WARNING: This page does not describe the selected car, but rather 31 other vehicles, including the 2006 Mercury Mountaineer, 2006 Mercury Monterey, 2006 Mercury Montego, 2006 Mercury Milan, and 2006 Mercury Mariner. However, it is still accessible from the selected car via links, so may be relevant.
The mechanical returnless fuel system consists of a fuel tank with reservoir, the fuel pump, the fuel pressure regulator, the fuel filter, the fuel supply line, the fuel rail, the fuel rail pulse damper (if equipped), fuel injectors, and a Schrader valve/pressure test point. For additional information on the fuel system components, refer to ENGINE CONTROL COMPONENTS . Operation of the system is as follows:
- The fuel delivery system is enabled during key ON, engine OFF for 1 second and during crank or running mode once the PCM receives a CKP sensor signal.
- The fuel pump logic is defined in the fuel system control strategy and is executed by the PCM.
- The PCM grounds the fuel pump relay, which provides power to the fuel pump.
- The inertia fuel shut-off (IFS) switch is used to de-energize the fuel delivery secondary circuit in the event of collision. The IFS switch is a safety device that should only be reset after a thorough inspection of the vehicle following a collision.
- A pressure test point valve (Schrader valve) is located on the fuel rail and is used to measure the fuel injector supply pressure for diagnostic procedures and repairs. On vehicles not equipped with a Schrader valve, use the Rotunda Fuel Pressure Test Kit 134-R0087 or equivalent.
- A pulse damper is located on the fuel rail (if equipped). The pulse damper reduces the fuel system noise caused by the pulsing of the fuel injectors. The vacuum port located on the damper is connected to manifold vacuum to avoid fuel spillage if the pulse damper diaphragm ruptures (the pulse damper should not be confused with a fuel pressure regulator).
- The fuel injector is a solenoid-operated valve that meters the 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 the 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.
- There are 3 filtering or screening devices in the fuel delivery system. The intake filter is a fine, nylon mesh screen 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. The fuel filter assembly is a 3-port filter that allows clean fuel to return to the fuel tank and is located between the fuel pump and the pressure test point/Schrader valve.
- The fuel pump (FP) module contains the fuel pump, the fuel pressure regulator, and the fuel sender assembly. The fuel pressure regulator is attached to the FP module and regulates the pressure of the fuel supplied to the fuel injectors. The fuel pressure regulator controls the pressure of the clean fuel as the fuel returns from the fuel filter. The fuel pressure regulator is a diaphragm-operated relief valve. Fuel pressure is established by a spring preload applied to the diaphragm. The FP module is located in the fuel tank.