System Operation
Fuel Systems
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.
Mechanical Returnless Fuel System (MRFS)
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 mechanical returnless fuel system (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.
Operation of the system is as follows:
Fuel Pump Control
The FP signal is a duty cycle command sent from the PCM to the fuel pump control module. The fuel pump control module uses the FP command to operate the fuel pump at the speed requested by the PCM or to turn the fuel pump OFF. A valid duty cycle to command the fuel pump ON, is in the range of 15-47%. The fuel pump control module doubles the received duty cycle and provides this voltage to the fuel pump as a percent of the battery voltage. When the ignition is turned ON, the fuel pump runs for about 1 second and is requested OFF by the PCM if engine rotation is not detected.
Fuel Pump Duty Cycle Output From PCM
FP Duty Cycle Command | PCM Status | Fuel Pump Control Module Actions |
0-5% | Invalid OFF duty cycle. | The fuel pump control module sends a 20% duty cycle signal on the FPM circuit. The fuel pump is OFF. |
5-47% | Normal operation. | The fuel pump control module operates the fuel pump at the speed requested. FP duty cycle times 1.43 minus 14.29 equals pump speed % of full ON. For example, FP duty cycle equals 42%. 42 times 1.43 minus 14.29 equals 46 (rounded). Pump is run at 46% of full ON. The fuel pump control module sends a 60% duty cycle signal on the FPM circuit. |
47-51% | Normal operation — full ON. | The fuel pump control module operates the fuel pump at full ON. The fuel pump control module sends a 60% duty cycle signal on the FPM circuit. |
51-67% | Invalid OFF duty cycle. | The fuel pump control module sends a 20% duty cycle signal on the FPM circuit. The fuel pump is OFF. |
67-83% | Valid OFF duty cycle. | The fuel pump control module sends a 60% duty cycle signal on the FPM circuit. The fuel pump is OFF. |
83-100% | Invalid OFF duty cycle. | The fuel pump control module sends a 20% duty cycle signal on the FPM circuit. The fuel pump is OFF. |
Fuel Pump Monitor (FPM)
The fuel pump control module communicates diagnostic information to the PCM through the FPM circuit. This information is sent by the fuel pump control module as a duty cycle signal. The duty cycle signals that may be sent are listed in the following tables.
Fuel Pump Control Module Duty Cycle Signals
Duty Cycle | Comments |
20% | This duty cycle indicates the fuel pump control module is receiving an invalid duty cycle from the PCM. |
60% | This duty cycle indicates the fuel pump control module is functioning normally. |
80% | This duty cycle indicates the fuel pump control module is detecting a concern with the secondary circuits. |
Fuel Filters
The system contains 3 to 5 filtering or screening devices.
Component Description
Fuel Pump (FP) Assembly
The FP assembly contains the fuel pump and sender assembly. The fuel pump is located inside the FP assembly reservoir and supplies fuel through the FP assembly manifold to the engine and FP assembly 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 Pump Control Module
The fuel pump control module receives a duty cycle signal from the PCM and controls the fuel pump operation in relation to this duty cycle. The PCM requests low or high speed fuel pump operation depending on engine fuel demand. The fuel pump control module controls the fuel pump by switching the fuel pump power circuit ON and OFF at the required duty cycle. The fuel pump control module sends diagnostic information to the PCM on the FPM circuit.
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 for 1 or 2 seconds, depending on application, as soon as the dome light is commanded ON. This causes the fuel pump control module and the fuel pump to cycle for 1 or 2 seconds and purge any trapped air or fuel vapor from the high pressure fuel system.
When the child safety locks are set, you cannot open the rear doors from the inside.
The child safety lock control is on the driver door.
Press the control to switch the child safety locks on. Press the control again to switch them off. A light on the child safety control illuminates when you switch them on.