Fuel Pump: Testing and Inspection

Schematic:

CIRCUIT DESCRIPTION
When you turn ON the ignition switch, the Powertrain Control Module (PCM) turns ON the in-tank fuel pump. The in-tank fuel pump remains ON as long as the engine is cranking or running and the PCM receives reference pulses. If there are no reference pulses, the PCM turns the in-tank fuel pump OFF 2 seconds after the ignition switch is turned ON or 2 seconds after the engine stops running.

The electric fuel pump attaches to the fuel sender assembly inside the fuel tank. The in-tank fuel pump supplies fuel through an in-pipe fuel filter to the fuel rail assembly. The fuel pump provides fuel at a pressure above the pressure needed by the fuel injectors. The fuel pressure regulator keeps the fuel available to the fuel injectors at a regulated pressure. The fuel pressure regulator attaches to the fuel sender assembly return pipe. Unused fuel returns to the fuel tank by a separate fuel return pipe. The fuel return pipe attaches to a T-connector in the fuel feed pipe on the outlet side of the fuel filter.

TEST DESCRIPTION

Steps 1 - 7:

Steps 8 - 12:

Steps 13 - 21:

The numbers below refer to the step numbers on the diagnostic table.
2. When the ignition switch is ON and the fuel pump is running, the fuel pressure indicated by the fuel pressure gauge should read 380-410 kPa (55-60 psi). The spring pressure inside the fuel pressure regulator controls the fuel pressure.
3. A fuel system that drops more than 34 kPa (5 psi) in 10 minutes has a leak in one or more of the following areas:
^ The fuel pipes.
^ The fuel pump check valve.
^ The fuel pump flex pipe.
^ The valve or valve seat within the fuel pressure regulator.
^ The fuel injector(s).
4. A fuel system that drops more than 14 kPa (2 psi) in 10 minutes after being relieved to 69 kPa (10 psi) indicates a leaking fuel pump check valve.
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 misfire. You can diagnose a lean condition using a scan tool. If an extremely lean condition occurs, the heated oxygen sensors(s) will stop toggling. The heated oxygen sensor output voltage(s) will drop below 300 mV. The fuel injector pulse width will increase.

IMPORTANT: Make sure the fuel system is not operating in the Fuel Cut-Off Mode. This can cause false indications by the scan tool.

10. A rich condition may result from the fuel pressure being above 410 kPa (60 psi). A rich condition may cause DTC P0132, DTC P0152, DTC P0172 or DTC P0175 to set. Driveability conditions associated with rich conditions can include hard starting followed by black smoke and a strong sulfur smell in the exhaust.
11. 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 faulty fuel pressure regulator.
12. A lean condition may result from the fuel pressure being below 380 kPa (55 psi). A lean condition may cause DTC P0131, DTC P0151, DTC P0171 or DTC P0174 to set. Driveability conditions associated with lean conditions can include hard starting (when the engine is cold), hesitation, poor driveability, lack of power, surging, and misfiring.

NOTE: Do not allow the fuel pressure to exceed 500 kPa (72 psi). Fuel pressure in excess of 500 kPa (72 psi) may damage the fuel pressure regulator.

13. Restricting the fuel return pipe with the J 37287 fuel pipe shut-off adapter causes the fuel pressure to rise above the regulated fuel pressure. Using a scan tool to pressure the fuel system, the fuel pressure should rise above 410 kPa (60 psi) as the valve on the fuel pipe shut-off adapter connected to the fuel return pipe becomes partially closed.
18. Check the spark plug associated with a particular fuel injector for fouling or saturation in order to determine if that particular fuel injector is leaking. If checking the spark plug associated with a particular fuel injector for fouling or saturation does not determine that a particular fuel injector is leaking, use the following procedure:
1. Remove the fuel rail, but leave the fuel pipe connected to the fuel rail. Refer to Fuel Rail Assembly Replacement.
2. Lift the fuel rail just enough to leave the fuel injector nozzles in the fuel injector ports.

CAUTION: In order to reduce the risk of fire and personal injury that may result from fuel spraying on the engine, verify that the fuel rail is positioned over the fuel injector ports. Also verify that the fuel injector retaining clips are intact.

3. Pressurize the fuel system by using the scan tool fuel pump enable.
4. Visually and physically inspect the fuel injector nozzles for leaks.