Fuel Systems
Fuel Systems
Overview
The fuel system supplies the sequential multi-port fuel injection (SF1) fuel injectors with clean fuel at a controlled pressure. The powertrain control module (PCM) controls the fuel pump and monitors the fuel pump circuit. The PCM controls the fuel injector on/off cycle duration and determines the correct timing and amount of fuel delivered. If the injectors have been replaced it is necessary to reset the learned values contained in the keep alive memory (KAM) in the PCM. Refer to Resetting The Keep Alive Memory (KAM).
The 3 types of fuel systems used are:
^ Returnable Fuel
^ Mechanical Returnless Fuel
^ Electronic Returnless Fuel
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:
1. The fuel delivery system uses the crankshaft position (CKP) sensor to signal the PCM that the engine is either cranking or running.
2. 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.
3. 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.
4. The inertia fuel shut-off (IFS) switch is used to de-energize the fuel delivery secondary circuit in the event of a collision. The IES switch is a safety device that should only be reset afier a thorough inspection of the vehicle following a collision.
5. 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.
6. 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.
7. The fuel pressure regulator is affached to the fuel rail downstream of the fuel injectors. It regulates the fuel pressure supplied to the fuel injectors. The fuel pressure regulator is a diaphragm-operated relief valve. One side of the diaphragm senses fuel pressure and the other side is connected to the intake manifold vacuum. Fuel pressure is established by a spring preload applied to the diaphragm. 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.
8. There are 4 filtering or screening devices in the fuel delivery system. The fuel intake filter 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.
9. 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.
Mechanical Returnless Fuel System
The mechanical retumless 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.
Operation of the system is as follows:
1. 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.
2. The fuel pump logic is defined in the fuel system control strategy and is executed by the PCM.
3. The PCM grounds the fuel pump relay which provides power to the fuel pump.
4. 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 afier a thorough inspection of the vehicle following a collision.
5. 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.
6. 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).
7. 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 crankshafi 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.
8. 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.
9. 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.
Electronic Returnless Fuel System
The electronic retumless fuel system consists of a fuel tank with reservoir the fuel pump the fuel rail pressure (FRP) sensor the fuel filter the fuel supply line the fuel rail temperature (FRT) sensor the fuel rail the fuel injectors and a Schrader valve/pressure test point. Operation of the system is as follows:
1. 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.
2. The fuel pump logic is defined in the fuel system control strategy and is executed by the PCM.
3. The PCM commands a duty cycle to the fuel pump driver module (FPDM).
4. The FPDM modulates the voltage to the fuel pump (FP) required to achieve the proper fuel pressure. Voltage for the fuel pump is supplied by the power relay or FPDM power supply relay.
5. The fuel rail pressure (FRP) sensor provides the PCM with the current fuel rail pressure. The PCM uses this information to vary the duty cycle output to the FPDM to compensate for varying loads.
6. The fuel rail temperature (FRT) sensor measures the current fuel temperatures in the fuel rail. This information is used to vary the fuel pressure and avoid fuel system vaporization.
7. 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.
8. 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.
9. 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 located between the fuel pump and the pressure test point/Schrader valve.
10. The fuel pump (FP) module is a device that contains 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.
11. The inertia fuel shut-off (IFS) switch is used to de-energize the fuel delivery secondary circuit in the event of a collision. The IES switch is a safety device that should only be reset afier a thorough inspection of the vehicle following a collision.
Fuel Pump Module and Reservoir
The fuel pump module is mounted inside the fuel tank in a reservoir. The pump has a discharge check valve that maintains the system pressure afier the ignition key has been turned off to minimize starting concerns. The reservoir prevents fuel flow interruptions during extreme vehicle maneuvers with low tank fill levels.
Fuel Pump Module
The fuel pump (FP) module is a device that contains the fuel pump and sender assembly. The fuel pump is located inside the FP module reservoir and supplies fuel through the FP module manifold to the engine and FP module jet pump. The jet pump continuously refills the reservoir with fuel and a check valve located in the manifold outlet maintains system pressure when the fuel pump is not energized. A flapper valve located in the bottom of the reservoir allows fuel to enter the reservoir and prime the fuel pump during the initial fill.
Fuel Filters
The system contains 4 filtering or screening devices. Refer to the individual component illustrations for locations.
1. The fuel intake filter or screen is a fine nylon mesh filter mounted on the intake side of the fuel pump. It is part of the assembly and cannot be repaired separately.
2. The filter/screen at the fuel rail port of the injectors is part of the fuel injector assembly and cannot be repaired separately.
3. The filter/screen at fuel inlet side of the fuel pressure regulator is part of the regulator assembly and cannot be repaired separately.
4. The fuel filter assembly is located between the fuel pump (tank) and the pressure test point (Schrader valve) or injectors. This filter may be replaced.
Pressure Test Point
On some applications there is a pressure test point with a Schrader fitting in the fuel rail that relieves the fuel pressure and measures the fuel injector supply pressure for repair and diagnostic procedures. Before repairing or testing the fuel system read any WARNING CAUTION and HANDLING information. On vehicles not equipped with a Schrader valve use the Rotunda Fuel Pressure Test Kit #134-R0087 or equivalent.
Fuel Injector
The fuel injector is a solenoid-operated valve that meters fuel flow to the engine. The fuel injector is opened and closed a constant number of times per crankshafi revolution. The amount of fuel is controlled by the length of time the fuel injector is held open.
NOTICE: Do not apply battery positive voltage (B+) directly to the fuel injector electrical connector terminals. The solenoids may be damaged internally in a matter of seconds.
The fuel injector is normally closed and is operated by 12-volt VPWR from the electronic engine control power relay. The ground signal is controlled by the PCM.
The injector is the deposit resistant injection (DRI) type and does not have to be cleaned. However it can be flow checked and if found outside of specification the fuel injector should be replaced.
Fuel Pressure Regulator
The fuel pressure regulator is attached to the fuel rail downstream of the fuel injectors. It regulates the fuel pressure supplied to the fuel injectors. The regulator is a diaphragm-operated relief valve. One side of the diaphragm senses the fuel pressure and the other side is connected to the intake manifold vacuum. Fuel pressure is established by a spring preload applied to the diaphragm. 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.
Fuel Rail Pulse Damper
The fuel rail pulse damper is located on the fuel rail and 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 fuel rail pulse damper should not be confused with a fuel pressure regulator; it does not regulate the fuel rail pressure.)