Fuel Systems: Notes

The fuel system supplies the fuel injectors with clean fuel at a controlled pressure. The 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. When a new fuel injector is installed it is necessary to reset the learned values contained in the KAM in the PCM.

The mechanical returnless fuel system (MRFS) can be configured with a dual or variable speed fuel pump. The MRFS incorporates a fuel pump control module which is used to control the speed of the fuel pump. The MRFS uses a fuel tank with reservoir, the fuel pump, the fuel pump control module, the fuel pressure regulator, the fuel filter, the fuel supply line, the fuel rail, and fuel injectors.

A pressure accumulator is incorporated into the fuel line to prevent fuel vapor formation after several hours of cold soak and reduce crank time.

• The fuel delivery system is enabled during PCM wake up for 1 second and during crank or running mode once the PCM receives a CKP sensor signal. For the PCM wake up circuit diagnostics, refer to STARTING SYSTEM - SYSTEM OPERATION AND COMPONENT DESCRIPTION . The high pressure fuel system may be under vacuum after several hours of cold soak. Fuel vapor may collect at the fuel injection pump, causing a long start condition. To prevent this, the fuel pump relay is energized, depending on application, when the PCM receives a calibrated signal. This causes the fuel pump control module and the fuel pump to cycle and purge any trapped air or fuel vapor from the high pressure fuel system.
• The fuel pump logic is defined in the fuel system control strategy and executed by the PCM.
• The fuel pump control module relay is located inside the battery junction box. The fuel pump control module relay provides voltage to the fuel pump control module.
• The PCM commands a duty cycle to the fuel pump control module. The fuel pump control module reports diagnostic information to the PCM. The fuel pump control module controls the voltage to the FP based on the duty cycle request from the PCM. Voltage for the fuel pump is supplied by the fuel pump control module relay.
• For vehicles with gasoline direct fuel injection, a fuel pressure sensor monitors the low pressure fuel system.
• For vehicles with gasoline direct fuel injection, the fuel injection pump raises fuel system pressure to as high as 15 MPa (2175 psi), and delivers it to the fuel rail.
• 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 fuel injector is normally closed and is operated by the PCM.
• There are 3 to 5 filtering or screening devices in the fuel delivery system.
• The FP assembly contains the fuel pump, the fuel pressure regulator, lifetime fuel filter and the fuel sender assembly. The fuel pressure regulator is attached to the FP assembly 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 assembly is located in the fuel tank.