Fuel Pump: Testing and Inspection

Fuel System Diagnosis:

Diagnostic Chart (Part 1 Of 3):

Diagnostic Chart (Part 2 Of 3):

Diagnostic Chart (Part 3 Of 3):

CIRCUIT DESCRIPTION
When the ignition switch is turned ON, the Powertrain Control Module (PCM) will turn ON the in-tank fuel pump. The in-tank fuel pump will remain ON as long as the engine is cranking or running and the PCM is receiving reference pulses. If there are no reference pulses, the PCM will turn OFF the in-tank fuel pump after 2 seconds because the ignition switch is turned ON, or after 2 seconds once the engine stops running. The in-tank fuel pump is an electric pump within an integral reservoir. The in-tank fuel pump supplies fuel through an in-line fuel filter to the fuel rail assembly. The fuel pump is designed to provide fuel at a pressure above the pressure that is needed by the fuel injectors. A fuel pressure regulator, attached to the fuel rail assembly, keeps the fuel available to the fuel injectors at a regulated pressure. The unused fuel is returned to the fuel tank by a separate fuel return pipe.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. In order to relieve the fuel pressure, go to Fuel Pressure Relief Procedure. When the ignition is ON and the fuel pump is running, the fuel pressure indicated by the fuel pressure gauge should be 284-325 kPa (41-47 psi).
3. A fuel system that drops more than 5 psi in 10 minutes has a leak in one or more of the following areas:
^ The fuel pump check valve
^ The fuel pump flex pipe
^ The fuel injectors
5. Fuel pressure that drops-off during acceleration, cruise, or hard cornering may cause a lean condition A lean condition can cause a loss of power, surging, or a misfire. You can use a scan tool in order to diagnose a lean condition. If an extremely lean condition occurs, the oxygen sensors will stop toggling. The oxygen sensor output voltages will drop to less than 500 mV. Also, the fuel injector pulse width will increase.
8. When the engine is idling, the manifold pressure is low, indicating high vacuum. This low pressure, or high vacuum, is applied to the fuel pressure regulator diaphragm. The low pressure, or high vacuum, will offset the pressure that is applied to the fuel pressure regulator diaphragm by the spring inside the fuel pressure regulator. This will cause lower fuel pressure. The fuel pressure at idle will vary slightly as the barometric pressure changes, but the fuel pressure at idle should always be less than the fuel pressure noted in step 2 with the engine turned OFF.
12. A rich condition may result from the fuel pressure being more than 325 kPa (47 psi). A rich condition can cause a DTC P0132 or a DTC P0172 to set. Driveability conditions that are associated with rich conditions can include hard starting followed by black smoke, and a strong sulfur smell in the exhaust.
13. This test determines if the high fuel pressure is due to a restricted fuel return pipe or if the high fuel pressure is due to a malfunctioning fuel pressure regulator.
15. Fuel pressure that is less than 284 kPa (41 psi) can cause a lean condition. A lean condition may cause a DTC P0131 or a DTC P0171 to set. Driveability conditions that are associated with lean conditions can include hard starting when the engine is cold, hesitation, poor driveability, a lack of power, surging, and misfiring.
16. Restricting the fuel flow causes the fuel pressure to be more than the regulated fuel pressure. Using a scan tool in order to pressurize the system, the fuel pressure should be more than 325 kPa (47 psi) as the gauge outlet hose is pinched.
22. Inspect the spark plug that is associated with a particular fuel injector for fouling or saturation in order to determine if that particular fuel injector is leaking.