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System Description

The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will disable the fuel pump relay within two seconds unless the control module detects ignition reference pulses. The control module continues to enable the fuel pump relay as long as ignition reference pulses are detected. The control module disables the fuel pump relay within two seconds if ignition reference pulses cease to be detected and the ignition remains ON.

The fuel tank stores the fuel supply. An electric turbine style fuel pump attaches to the fuel pump module inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter and the fuel feed pipe to the fuel injection system. The fuel pump provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pump also supplies fuel to a venturi pump located on the bottom of the fuel pump module. The function of the venturi pump is to fill the fuel pump module reservoir. The fuel pressure regulator, a part of the fuel pump module, maintains the correct fuel pressure to the fuel injection system. The fuel pump module contains a reverse flow check valve. The check valve and the fuel pressure regulator maintain fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.

Fuel System Diagnosis

Step Action Values Yes No
1 Did you perform the Diagnostic System Check - Vehicle? - Go to Step 2  Go to Diagnostic System Check - Vehicle
2
    IMPORTANT: Inspect the fuel system for damage or external leaks before proceeding with this diagnostic.
  1. Turn ON the ignition, with the engine OFF.
  2. Command the fuel pump relay ON with a scan tool.
Does the fuel pump operate?		 - Go to Step 3  Go to Fuel Pump Electrical Circuit Diagnosis 
3
IMPORTANT: Verify that adequate fuel is in the fuel tank before proceeding with this diagnostic.
  1. Turn OFF the ignition.
  2. Turn OFF all accessories.
  3. Install the SA9127E  Gage Bar Set with the Fuel Pressure Adapter and the Drain Hose. See Special Tools . Refer to Fuel Pressure Gage Installation and Removal .
  4. Turn ON the ignition, with the engine OFF.
    5. IMPORTANT: DO NOT start the engine.
  5. Command the fuel pump relay ON with a scan tool.
  6. Observe the fuel pressure gage with the fuel pump commanded ON.
Is the fuel pressure within the specified range?		 345-414 kPa (50-60 psi) Go to Step 5  Go to Step 4 
4 Is the fuel pressure more than the specified value? 414 kPa (60 psi) Go to Step 11  Go to Step 8 
5
IMPORTANT: The fuel pressure may vary slightly when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize and remain constant.
Monitor the fuel pressure gage for 5 minutes.Does the fuel pressure decrease by more than the specified value?		 55 kPa (8 psi) Go to Step 7  Go to Step 6 
6
  1. Operate the vehicle within the conditions to reproduce the original symptoms.
  2. Monitor the O2 and the Fuel Trim parameters with a scan tool.
Does the scan tool parameters indicate a lean condition?		 - Go to Step 8  Go to Symptoms - Engine Controls 
7
  1. Turn OFF the ignition.
  2. Relieve the fuel pressure. Refer to Fuel Pressure Relief Procedure .
  3. Remove the fuel pressure gage from the fuel pressure test connection.
  4. Raise the vehicle. Refer to Lifting and Jacking the Vehicle .
  5. Disconnect the fuel feed pipe and the fuel return pipe from the fuel filter. Refer to Quick Connect Fitting(s) Service (Plastic Collar) (Press Release) .
  6. Connect the fuel feed pipe to the inlet side of SA9127E-7  Fuel Pressure/Flow Adapter. See Special Tools .
  7. Connect the fuel return pipe to the ON/OFF valve side of the SA9127E-7  . See Special Tools .
  8. Connect the fuel pressure gage to the SA9127E-7  . See Special Tools .
  9. Open the valve on the SA9127E-7  . See Special Tools .
  10. Turn ON the ignition, with the engine OFF.
  11. Command the fuel pump relay ON for a minimum of 10 seconds with a scan tool.
  12. Close the valve on the SA9127E-7  . See Special Tools .
  13. Monitor the fuel pressure gage for 5 minutes.
Does the fuel pressure decrease by more than the specified value?		 55 kPa (8 psi) Go to Step 11  Go to Step 10 
8 Inspect the following components for a restriction:
  • The fuel filter
  • The fuel feed pipe

Did you find and correct the condition?		 - Go to Step 12  Go to Step 9 
9 Inspect the harness connectors and the ground circuits of the fuel pump for poor connections. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 - Go to Step 12  Go to Step 11 
10
  1. Turn OFF the ignition.
  2. Raise the fuel rail with the fuel pipe connected. Refer to Fuel Rail Assembly Replacement .
  3. Turn ON the ignition, with the engine OFF.
  4. Command the fuel pump relay ON with a scan tool.
  5. Locate and replace the leaking fuel injector. Refer to Fuel Injector Replacement .
Did you complete the replacement?		 - Go to Step 12  -
11 Replace the fuel pump module. Refer to Fuel Pump Module Replacement .
Did you complete the replacement?		 - Go to Step 12  -
12 Operate the system in order to verify the repair.
Did you correct the condition?		 - System OK Go to Step 3 
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