GMC 25163468 Fuel Pump

For undertaking the fuel pressure test get a fuel pressure gauge coupled with a fuel injection system adapter. Start with a visual inspection performing a rundown check with fuel on the tank, check at the threaded ends of the fuel line for leaks while the engine is running; check for tight connections, flatten or kinks of hoses. Following this, release the fuel system pressure. For models with port fuel injection as required, position the gauge over the Schrader valve of the fuel rail, turn the ignition ON with the Aircon OFF, and take the reading when the fuel pump has its cycle for 2 seconds. The pressure should be maintained constant to the values available within the set range. Switch on the engine for some time and allow it to warm; the pressure should reduce by 3-10 psi. If it does not then add 10 inches vacuum to the pressure regulator and look for pressure drop to know if the regulator needs repair or replacement. If pressure is not within specs consult fuel filter & hoses, pressure regulator, fuel line for leaks & the in-tank fuel pump check valve. Upon completion of the test, turn off the fuel pump and then, switch off the ignition to relieve fuel pressure and then unscrew the gauge. For models with throttle body injection, turn the ignition off for at least twenty seconds, release the fuel pressure, connect a fuel pressure gauge between the fuel hose and the throttle body inlet and use a fused jumper wire when testing the pressure. If the pressure is within the requirements, then no more test is required if not then look for restricted lines or problem with the regulator. After that, it is required to turn off the fuel pump, release fuel pressure, and, finally, take out the gauge. If there are suspicions that there are problems with the fuel pump, check whether you can hear the noise at the moment when the switch is turned On and during the start of the engine. If the pump does not activate, then look at the fuse and the relay of the fuel pump on your car. To test the relay unscrew it while the engine is on; in case the engine continues to run then the oil pressure switch may be a problem. Connect back the relay and touch the terminal for fuel pump with a test light to check the circuit.

The fuel pump is a high pressure electric one equipped in the fuel tank, impeller works as the vapor preventer and pre-charges high pressure assembly. Fuel is delivered at positive pressure through an in line fuel filter to the fuel rail assembly, the pressure regulator keeps the pressure required by injectors and any excess fuel is returned to the fuel tank through fuel return line. The electric pump connected in parallel with the PCM and operates whenever the ignition is 'on' and the engine is cranking or running; it turns off immediately the engine cuts or the starter is removed within one second. To remove and install on 4.5L and 4.9L engines, turn off the ignition, disconnect the negative battery terminal, discharge the fuel system, lift the front part of the vehicle and then un bolt the fuel tank, to get access to the pump, turn counter clockwise the cam lock ring to lift the assembly out. To remove it, one has to pull the pump up and at the same time pull it outwards taking care not to break the rubber insulator or the strainer which is always stuck beside it. Installation requires removal of all damaged hoses, forcing the pump into the hoses, employing a brand new O-ring seal, and checking the strainer does not encumber the float arm. For the 4.6L engine, there is integrated fuel sender assembly, which contains fuel pump; it is very difficult to repair due to the use of special tools. Do not fill the tank to the full whenever you want to access the sender with a view of avoiding spilling of fuel. Once you have taken off the fuel rail pressure and has disconnected the battery, then try to find out whether the tank needs to be dropped or whether the access is possible at the rear. If possible, lower the tank, and take off the spare tire lid and rear emblem, unbolt quick connect hoses and electrical plugs, spanner wrench for the ring. Upon removal the sender assembly must be tilted slightly in order to avoid sending the floats out of alignment. Remove the strainer and O-ring and before fitting the new one ensure that the strainer does not hinder the float arm from moving. Reinstalling the battery require checking for any form of leaking during the cycling of the ignition and at the same tightening the access panel bolts. The in-tank pump works when the ignition is on and will remain on during any engine running or cranking, and it will shut down should it fail to detect any reference pulses.

The fuel pump is a high pressure electric one equipped in the fuel tank, impeller works as the vapor preventer and pre-charges high pressure assembly. Fuel is delivered at positive pressure through an in line fuel filter to the fuel rail assembly, the pressure regulator keeps the pressure required by injectors and any excess fuel is returned to the fuel tank through fuel return line. The electric pump connected in parallel with the PCM and operates whenever the ignition is 'on' and the engine is cranking or running; it turns off immediately the engine cuts or the starter is removed within one second. To remove and install on 4.5L and 4.9L engines, turn off the ignition, disconnect the negative battery terminal, discharge the fuel system, lift the front part of the vehicle and then un bolt the fuel tank, to get access to the pump, turn counter clockwise the cam lock ring to lift the assembly out. To remove it, one has to pull the pump up and at the same time pull it outwards taking care not to break the rubber insulator or the strainer which is always stuck beside it. Installation requires removal of all damaged hoses, forcing the pump into the hoses, employing a brand new O-ring seal, and checking the strainer does not encumber the float arm. For the 4.6L engine, there is integrated fuel sender assembly, which contains fuel pump; it is very difficult to repair due to the use of special tools. Do not fill the tank to the full whenever you want to access the sender with a view of avoiding spilling of fuel. Once you have taken off the fuel rail pressure and has disconnected the battery, then try to find out whether the tank needs to be dropped or whether the access is possible at the rear. If possible, lower the tank, and take off the spare tire lid and rear emblem, unbolt quick connect hoses and electrical plugs, spanner wrench for the ring. Upon removal the sender assembly must be tilted slightly in order to avoid sending the floats out of alignment. Remove the strainer and O-ring and before fitting the new one ensure that the strainer does not hinder the float arm from moving. Reinstalling the battery require checking for any form of leaking during the cycling of the ignition and at the same tightening the access panel bolts. The in-tank pump works when the ignition is on and will remain on during any engine running or cranking, and it will shut down should it fail to detect any reference pulses.

The fuel pump is a sealed type actuated by the engine camshaft, utilizing a pushrod between the camshaft and the pump rocker in Chevrolet-manufactured engines. While servicing is not possible due to the sealed nature of the unit, a test can be performed if a fault is suspected. First, ensure there is gas in the fuel tank. Then, disconnect the primary wire running between the coil and the distributor to prevent engine firing when the starter motor is engaged for 1974 models; for 1975 to 1980 models, disconnect the distributor wiring marked 'BAT.' Next, disconnect the fuel inlet pipe from the carburetor and place its open end in a container. Operate the starter motor and observe for well-defined spurts of fuel ejected from the open end of the pipe. If spurts are present, the pump is functioning correctly; if not, replacement of the pump is necessary.

To check the fuel pump output and pressure, relieve the fuel pressure. Next, Install a fuel pressure gauge on the fuel rail, location varies depending on the 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 the pressure does not drop as expected, apply a 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. 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.

In order to remove the pump, unbolt the inlet and outlet pipes to the pump by the use of two wrenches in order not to cause damage to the pump and connections. Secondly, remove the fuel pump mounting bolts, the actual pump, as well as the gasket. When replacing the new pump, the new gasket should be used together with conventional gasket sealant around the screw threads. Lastly, join the fuel pipes, switch on the engine and examine if there is any leakage.

To conduct a fuel pressure test, you'll need a fuel pressure gauge and appropriate adapter. First, ensure fuel is present and inspect for leaks. Attach the gauge to the fuel rail's Schrader valve, turn on the ignition, and observe the reading. Start the engine and check if the pressure drops by 3-10 psi. If not, apply vacuum to the regulator. If the pressure isn't correct, examine the fuel components. Afterward, release the pressure and remove the gauge. For Throttle Body Injection models, install the gauge between the fuel hose and throttle body. Using a jumper, observe the reading. If the pressure is off, inspect for restrictions or malfunctioning components. Finally, listen for the fuel pump's noise when starting. If it's silent, check the fuse and relay. Apply 12 volts to the pump's terminal to verify functionality. If it's non-operational, inspect the relay and pump circuit.

Ensure that there is enough fuel in the tank and relieve the fuel pressure.

The first step is to relieve the fuel system pressure and disconnect the cable from the negative battery terminal.

The first step is to relieve the fuel system pressure and disconnect the cable from the negative battery terminal.