Returnable Fuel System
WARNING: This page is about a different variant/trim than selected.
Returnable fuel system consists of a fuel tank with a reservoir, fuel pump module, fuel supply lines, fuel filter(s), Schrader/pressure test port, fuel rail, fuel injectors, and fuel pressure regulator. The following list of components and their specific operation corresponds to numbers in illustration. See Fig 1.
- The fuel delivery system uses Crankshaft Position (CKP) sensor to signal PCM that engine is either cranking or running.
- The fuel pump logic is defined in Fuel System control strategy and is executed in PCM. PCM will ground fuel pump relay for one second during Key On Engine Off. During cranking, fuel pump relay is grounded as long as PCM receives a CKP signal.
- The fuel pump relay has a primary and a secondary circuit. Primary side is controlled by PCM and secondary side provides battery voltage (B+) to fuel pump circuit when relay is energized.
- 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) .
- 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.
- 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 pressure regulator is attached to fuel rail downstream of fuel injectors. It regulates fuel pressure supplied to fuel injectors. Fuel pressure regulator is a diaphragm operated relief valve. See Fig 2. One side of diaphragm senses fuel pressure and the other side is connected to intake manifold vacuum. Fuel pressure is established by a spring preload applied to diaphragm. Balancing one side of diaphragm with manifold vacuum maintains a constant fuel pressure drop across fuel injectors. Fuel pressure is high when engine vacuum is low. Excess fuel is by-passed through fuel pressure regulator and returned through a fuel return line to fuel tank.
- There are 4 filtering or screening devices in fuel delivery system. Fuel intake sock or screen is a fine, nylon mesh mounted on intake side of fuel pump. See Fig 3. There is a fuel filter screen located at fuel rail side of fuel injector. A fuel filter/screen is located in the inlet side of fuel pressure regulator. The fuel filter assembly is located between fuel pump and pressure test point/Schrader valve.
- The Fuel Pump (FP) module is a device that contains both fuel pump and fuel sender assembly. The fuel pump is located inside reservoir and supplies fuel through fuel pump module manifold to engine and fuel pump module jet pump. See Fig 4. The fuel pump also has a discharge check valve to maintain system pressure during shutdowns and to minimize starting problems. The reservoir prevents fuel flow interruptions during extreme vehicle maneuvers with low tank fill levels.
Courtesy of FORD MOTOR CO.
