GM 25163468 Fuel Pump

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Apply vacuum to the pressure regulator and if it drops, repair the vacuum source or replace the regulator.

The fuel pump should be reassembled to the sending unit bracket assembly and then inserted back into the fuel tank.

To check the fuel pump output and pressure, first ensure that there is enough fuel in the tank and relieve the fuel pressure. Then, install a fuel pressure gauge on the fuel rail, with the location varying depending on the type of system. Turn the ignition switch on without starting the engine and note the reading on the gauge as the fuel pump runs for about two seconds. The pressure should hold steady within the specified range. Start the engine and let it idle at normal operating temperature, with the pressure expected to be lower by 3 to 10 psi. If all pressure readings are within the limits, the system is operating properly. If the pressure does not drop as expected, apply vacuum to the pressure regulator and if it drops, repair the vacuum source or replace the regulator. If the pressure is not within specifications, check for a vacuum to the regulator or a pinched/clogged fuel return hose. If the pressure is still low, change the fuel filter and if it remains low, install a fuel line shut-off adapter to test the regulator. If the pressure is still low with the return line restricted, there may be a leaking injector or a faulty fuel pump. After testing, relieve the fuel pressure and remove the gauge. To check the fuel pump's electrical circuits, verify that the pump runs by listening for a whirring noise when the ignition switch is turned on and when the engine is started. Check the fuel pump fuse and the fuel pump relay circuit, ensuring there is battery voltage at the relay connector. Replace the relay if necessary and check for power to the fuel pump at the tank.

In order to perform a fuel pressure test, you will need a fuel pressure gauge and adapter set for the fuel injection system being tested. For a preliminary inspection, always ensure there is fuel in the tank and inspect for leaks at the threaded fittings and hoses. To check the pressure, relieve the fuel system pressure and install a fuel pressure gauge at the Schrader valve on the fuel rail. Turn the ignition switch on and note the reading on the gauge. Start the engine and let it idle, checking that the pressure is lower by 3 to 10 psi. If the pressure did not drop, apply vacuum to the pressure regulator. If the pressure is not within specifications, check the fuel filter, hoses, pressure regulator, fuel line, vacuum hose, and injectors. After testing, relieve the fuel pressure and remove the gauge. For models with Throttle Body Injection, relieve fuel system pressure and install a fuel pressure gauge between the fuel feed hose and the inlet fitting of the throttle body. Use a fused jumper wire to jump the fuel pump test terminal and note the pressure reading. If the pressure is within limits, no further testing is necessary. If the pressure is higher, check for a restricted fuel return line or replace the pressure regulator. If the pressure is lower, pinch the hose and note the pressure. If the pressure goes above 9 psi, replace the pressure regulator. If there is no pressure, check for a plugged fuel filter, pump inlet filter, or restricted fuel line. After testing, relieve the fuel pressure and remove the gauge. To check the fuel pump, verify that it runs by listening for a whirring noise when the ignition is turned on and a constant whirring sound when the engine is started. If the pump does not come on, check the fuel pump fuse and relay. If the fuse is blown, replace it and test the pump. If the pump still does not work, apply 12 volts to the fuel pump test terminal and listen for the pump running. If the pump runs, check the fuel pump relay. If the pump does not run, check for an open circuit between the relay and the fuel pump.

The assembly can be released by carefully tapping the locking cam until the tabs align with the recesses.