Fuel Pump: Testing and Inspection

Diagnostic Chart 1 Of 2:

Diagnostic Chart 2 Of 2:

Schematic:

SYSTEM DESCRIPTION
The Powertrain Control Module (PCM) will energize the fuel pump relay for 2 seconds when the ignition switch is turned to the ON position. The fuel pump will operate and pressurize the fuel system when the fuel pump relay is energized. The PCM receives ignition system reference pulses when the engine is cranked or running. The PCM will continue to energize the fuel pump relay as long as the PCM receives ignition system reference pulses. The PCM will de-energize the fuel pump relay when ignition system reference pulses are no longer detected.

The fuel pump delivers fuel to the fuel injectors in the fuel rail at a controlled pressure. The controlled pressure is 270-310 kPa (38.5-44 psi) when the fuel pump is energized and the engine is not running. The controlled pressure is 200-240 kPa (28.5-34 psi) when the engine is idling at normal operating temperatures. The fuel-pressure regulator maintains the correct fuel pressure at all times by returning excess fuel to the fuel tank.

DIAGNOSTIC AIDS
Incorrect fuel system pressure can result in any of the following conditions:
^ The engine cranks but will not start.
^ The engine cuts out or stalls. This may feel like an ignition malfunction.
^ A decrease in fuel economy and a decrease in power.
^ Hard starting

Check for water contamination of the fuel if the vehicle will not start in freezing weather. Ice can form in the fuel system and prevent the fuel from reaching the fuel injectors at the necessary fuel pressure and at the necessary volume.

The normal fuel pump electrical resistance is 0.8-1.5 ohms at 20°C (68°F).

An intermittent malfunction may be caused by a fault in the fuel pump electrical circuit. Inspect the wiring harness and the components for any of the following conditions:
^ Backed out terminals.
^ Incorrect mating of terminals.
^ Broken electrical connector locks.
^ Incorrectly formed terminals or damaged terminals.
^ Any faulty terminal to wire connections.
^ Physical damage to the wiring harness.
^ A broken wire inside the insulation.
^ Corrosion of electrical connections, of electrical splices, or of terminals.

TEST DESCRIPTION
The numbers below refer to the step numbers in the diagnostic table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks, and to save the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data that was taken when the fault occurred. The scan tool saves the information for later reference.
3. This step checks if fuel system pressure is meeting specifications. The ignition must be ON, and the fuel pump must be running. The Output Control on the scan tool can operate the fuel pump when the fuel level is more than 20 percent, and no DTCs are set.
4. This step checks the fuel pressure after the fuel pump stops. Approximately one minute after the fuel pump stops, fuel pressure should remain steady at 200 kPa (28.5 psi). The Output Control on the scan tool can operate the fuel pump when the fuel level is more than 20 percent, and no DTCs are set.
5. The vehicle should start and run. Adequate fuel pressure is available for the engine to operate. A vehicle that will not start may have inoperative injectors. Check the fuel injectors and the fuel injector circuitry. Refer to Fuel Injector Circuit Diagnosis. Component Tests and General Diagnostics
6. This step checks for normal fuel pressure when the engine is running. Fuel pressure that is not within the specified value indicates a possible fault in the fuel pressure regulator.
8. This step checks for a faulty check valve in the fuel pump. The Output Control on the scan tool can operate the fuel pump when the fuel level is more than 20 percent, and no DTCs are set.
9. This step checks for a faulty check valve in the fuel pump. Blocking the fuel feed hose between the fuel pressure gauge and the fuel pump, traps the fuel pressure. The pressure becomes trapped between the fuel pressure regulator and the blocked section of the fuel feed hose. Immediately after the fuel pump stops, block the fuel feed hose. If fuel pressure now remains above the specified value, the fault is between the blocked section and the fuel tank. The Output Control on the scan tool can operate the fuel pump when the fuel level is more than 20 percent, and no DTCs are set.
12. This step checks for a faulty fuel pressure regulator. The Output Control on the scan tool can operate the fuel pump when the fuel level is more than 20 percent, and no DTCs are set.
13. A fault in the fuel pump electrical circuit may be caused by low fuel pressure or by zero fuel pressure. Go to the Fuel Pump Electrical Circuit Diagnosis in order to diagnose the fuel pump electrical circuit. Component Tests and General Diagnostics
14. This step checks for conditions except for a faulty fuel pump that can cause low fuel pressure. Check for any restrictions or for any blockages in the fuel feed lines and in the hoses, including those inside the fuel tank. Check the fuel pump electrical circuit for excessive resistance. Correct fuel pump operation requires correct voltage and adequate current flow.
15. This step checks the operation of the fuel pressure regulator. The Output Control on the scan tool can operate the fuel pump when the fuel level is more than 20 percent, and no DTCs are set.