GMC 25163468 Fuel Pump

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.

To remove the fuel pump/sending unit assembly, first, the fuel pressure should be relieved and the cable separated from the negative terminal of the battery, it is also useful to lock out the Delco Loc II audio system of the car if at all engaged. Thirdly, dismantle the fuel tank as the assembly is fitted in the tank and could only be accessed by undoing a cam lock ring mechanism of inner ring with three locking cams and outer ring with three retaining tangs. Loosen the assembly by turning the internal flange anti clockwise until the locking lugs are free: be careful not to damage float mechanism in this process. When it is free, simply pull the assembly out of the tank carefully to not that break the delicate fuel level float and sending unit. Ensure the rubber gasket round the lock ring mechanism is in good condition and if not replace it. Bend down and look at the fuel pump filter, if it is dirty, then clean it with solvent and compressed air or better still replace the filter if it is too dirty. If disconnecting the fuel pump and sending unit: while loosening the pump assembly in the rubber connector be gentle in order not to crack the rubber insulator or damage the fuel strainer. To reinstall the assembly, screw the fuel pump/sending unit back into the fuel tank by turning the inner lock ring counter clockwise; note that if a new O-ring has been installed one may have to push down on the inner lock ring in order to engage it before reinstalling the fuel tank.

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.

Inspect the fuel filter, hoses, pressure regulator, fuel line for leaks, and the in-tank fuel pump check valve.

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.

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

A test can be performed by following these steps: 1. Ensure there is gas in the fuel tank. 2. For 1974 models, disconnect the primary wire running between the coil and the distributor to prevent engine firing when the starter motor is engaged. For 1975 to 1980 models, disconnect the distributor wiring marked 'BAT.' 3. Disconnect the fuel inlet pipe from the carburetor and place its open end in a container. 4. Operate the starter motor and observe for well-defined spurts of fuel ejected from the open end of the pipe.