Fuel Pump

Fuel pump replacement:

• • Dropping the tank is not as hard as some make it out to be.

  • Always, always, always replace the fuel filter when changing the fuel pump(and I will say it again later).

  • Personally, I wouldn't cut a hole in my floor to access the fuel pump except under very specific circumstances.

  • Very few tools are needed to drop the tank and replace the pump.

  • If you know that it's failing, order your pump/sender and run the tank as close to empty as you can, it makes a huge difference in weight when dropping the tank. Remember gasoline weighs about 6.3lbs per gallon(170lbs extra on some models).

  • Don't forget to replace the in-line fuel filter(under drivers seat, near frame rail) and the filter sock(bottom of pump) when changing the fuel pump. This is important for the life of your new pump.

  • The tank should be cleaned, inspected and flushed while it's down as well.

  • Always keep a dry chemical fire extinguisher handy when performing any fuel related work.

Fuel pump pressure testing:

See parent page Fuel System

Fuel pump electrical circuit schematics and diagnostics:

See Manuals_and_Docs and if you have a 96 and up, get the GM Techline eSI already ;)

Example of a 96 fuel pump wiring diagram:

Example of a 99 fuel pump wiring diagram(later models are basically the same).

1st Generation fuel pump circuit examples: See video as well https://www.youtube.com/watch?v=xd4dDVWECUY

It works basically the same way for all models that have the fuel pump circuit going through the oil pressure switch(3 prong sender), through 1998 Astro/Safari vans.

Examples of single prong and three prong sensor connectors(the single prong sensor does NOT have the fuel pump circuit going through it).

1st Gen fuel pump circuit:

In the diagram above, orange is always hot, and the red is energized for prime and whenever the engine is running(even without oil pressure).

Once the engine builds oil pressure(above 4psi), the oil pressure switch enables a second route to power the fuel pump.

Would low oil pressure cause the fuel pump to shut off?

On the models that run parallel circuits to power the fuel pump, the pump can be turned on using the fuel pump relay and there is a backup path to power the fuel pump through the oil pressure switch. In the 98 and earlier models that are wired that way, as long as the ECM/PCM are receiving a signal from the CPS, it will keep the fuel pump relay energized regardless of the oil pressure switch. Now if you have a bad fuel pump relay or connection, then it's possible that a loss of oil pressure (under 4psi), a bad oil pressure switch, or disconnecting the connector at the oil pressure sensor/switch would expose that problem to you. But this would also be noticeable as a longer cold start cranking time and lack of fuel pump prime when the ignition is turned to run.

Do I have to replace the fuel sending unit at the same time?

Not necessarily, while the factory and most aftermarket pumps for the later models come as a complete set, you can indeed replace just the fuel pump itself.

Walbro 255l/h pump http://amzn.to/2opOpOb

Possible temporary inline external fuel pump solution:

Note: i have not yet tried this, still searching for the best solution.

Factory fuel line is 3/8 to the fuel filter with m16x1.5 threads to and from the filter.

Line from tank going to filter, 3/8-m16x1.6 line to new filter, 3/8 barb adapter to external pump, to 3/8 barb adapter to existing filter.

• • Dorman 3/8 barb to fuel filter x2 https://amzn.to/2T2Rp0h

  • Fuel filter for vehicle(03) https://amzn.to/2AZ0W1r

  • External fuel pump 60 gph/227 lph and 90 psi rating or better. https://amzn.to/2Df3VEm

  • 3/8 FI hose to connect everything together

  • Electrical connector for factory fuel pump connection(won't connect level gauge)