Oldsmobile 25168719 Fuel Pump

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To test the fuel pump relay, disconnect it and connect a test light to the ignition wire.

The process for replacing a mechanical pump on carbureted models involves disconnecting the battery cable, detaching the fuel inlet hose, outlet line, and vapor return hose, removing the mounting bolts, and retrieving the pushrod. After cleaning the block mounting surface and applying grease to the pushrod, the new gasket and pump are installed and the hoses and lines are reattached. For electric pumps on fuel-injected models, the fuel system pressure is relieved and the fuel tank is removed. The fuel pump/sending unit assembly is unlocked by turning the inner ring counterclockwise, and then lifted from the tank. The rubber gasket and strainer are inspected and replaced if necessary. If needed, the fuel pump can be separated from the sending unit. The assembly is then inserted back into the fuel tank and the inner lock ring is turned clockwise to engage the locking cams. Finally, the fuel tank is installed.

If fuel pressure is too low, you should conduct a fuel pump volume check, and if volume is insufficient, inspect for fuel line restrictions. If no restrictions are found, replace the fuel pump.

Check for restrictions in fuel lines and filters, and inspect the fuel pump for issues.

To begin, disconnect the negative battery cable to isolate the battery.

Inspect the condition of the seal around the mouth of the lockring mechanism.

Check for restrictions in fuel lines and filters, and inspect the fuel pump for issues.

On models equipped with the Theftlock audio system, be sure the lockout feature is turned off before performing any procedure that requires disconnecting the battery. This is to prevent any issues with the audio system.

After that, the fuel tank needs to be removed.

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

After cleaning the block mounting surface and applying grease to the pushrod, the new gasket and pump should be installed and the hoses and lines should be reattached.

To test the fuel pump, start by disconnecting the fuel line into the carburetor and then crank the engine. Check if there is a strong spurt of gasoline from the line. If not, inspect for clogs or issues with the fuel pump. To test the fuel pump flow capacity, use a measuring container and a watch to see if the pump can pump one pint of gasoline in 30 seconds or less.

There may be a leaking injector or a faulty fuel pump.

The fuel pump for both four-cylinder and V6 powered models is located in the fuel tank and is not repairable. When the key is turned on without the engine running, the ECM activates the fuel pump relay for two seconds to build up fuel pressure quickly. If the engine is not started within this time, the ECM waits until the engine starts, and then the relay runs the fuel pump. Additionally, the fuel pump can be activated by the oil pressure switch as a backup system if the fuel pump relay fails. An inoperative fuel pump relay can lead to long cranking times, especially when the engine is cold, and the oil pressure switch serves as a backup to activate the fuel pump when oil pressure reaches about 4 psi. The ECM turns on the in-tank fuel pump when the ignition is turned to On, and it remains on as long as the engine is cranking or running and the ECM receives HEI distributor reference pulses. To test the fuel pump operation, a fuel pressure gauge is installed, and the ignition is turned to the On position, where the fuel pump should run for two seconds and pressurize the system at specified levels. If there is no fuel pressure, the fuel pump fuse and associated wiring should be checked. If the fuse is good but there is no fuel pressure, the fuel pump can be checked by applying battery voltage to the fuel pump test terminal while listening for operation or checking for restrictions in the fuel delivery line or a clogged fuel filter. If the fuel pressure is not within specified limits, further tests are conducted to identify faulty components like the fuel pump, fuel line coupling hose, or fuel pressure regulator. Leaks in the fuel system, including injectors and valves, are also checked and addressed accordingly. The fuel pump relay and connector should be inspected for burned or loose wires if there is no fuel pressure and the fuel pump fuse is good.

For fuel-injected models, start by verifying that the fuel pump is running by listening for a whirring noise when the ignition switch is turned on. If the pump does not come on, check the fuel pump fuse and relay. If they are both functioning properly, check for an open circuit between the relay and the fuel pump. If the circuit is fine, disconnect the electrical connector at the fuel pump and connect battery voltage to the gray wire terminal of the pump to see if the pump runs.

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

To remove the fuel pump/sending unit assembly, start by disconnecting the cable from the negative battery terminal. Then, relieve the fuel pressure. Next, remove the fuel tank. Inside the fuel tank, the fuel pump/sending unit assembly is held in place by a lockring mechanism. To unlock it, turn the inner ring clockwise until the locking cams are free of the retaining tangs. If the rings are too tight, gently knock them loose with a soft-face hammer. Carefully extract the fuel pump/sending unit assembly from the fuel tank, making sure not to bump it into the outer lockring. Inspect the condition of the rubber gasket and replace it if necessary. Also, inspect and clean the strainer on the lower end of the fuel pump. If needed, separate the fuel pump from the sending unit by pulling the pump assembly into the rubber connector and sliding it away from the bottom support. Take care not to damage the rubber insulator and fuel strainer. For installation, insert the fuel pump/sending unit assembly back into the fuel tank and turn the inner lockring counterclockwise until the locking cams are fully engaged by the retaining tangs. Finally, reinstall the fuel tank.

The final step is to install the fuel tank.