How to replace your fuel pump

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Chief Knuckle Buster
Jun 16, 2009
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Greater Seattle
Hey all!! First real post here. I just bought a 1999 4dr, 4wd, shaved, 4" suspension lifted on 33x12.5R15's, custom blue ** for my wife from a guy who really abused it. So far in the couple weeks we've had it, it has left my wife stranded twice, needing a new alternator, and a new fuel pump. It also needed new everything brakes. I couldn't find anyone with any info on how to swap the fuel pump, and the haynes manual was pathetically inaccurate. So here's how I did it for the cost of parts ($250), saving a good $600.

You need:
  • Metric socket set
  • 2 crescent wrenches
  • Flat head screwdriver
  • Jack Stands, or other large blocks to hold up the fuel tank
  • Wire cutters
  • Wire Connection Crimpers
  • Wire Strippers
  • Pressure fitting disconnector tool (rent from O’Reilly for a couple bucks)
  • Hammer
  • Buddy to laugh at you, drink your beer, and turn the ignition on once in a while
  • Beer
  • Fuel Pump Relay (~$8)
  • Fuel Filter (~$10)


Replace the fuel filter (need to do it anyway, to keep the pump warranty):
  1. Disconnect the negative/ground cable from the battery
  2. Find the filter under the driver’s side, just in front of the fuel tank, inside the frame rail.
  3. Unscrew it, involuntarily get gas in your mouth, eyes, nose, and screw the new one in.

Replace the fuel pump relay:
  1. Under the hood, driver’s side, halfway back, under the “Relay Panel.” Sitting in the driver’s seat, it would be the 1” x 1” cube furthest from you, furthest to the right, with 5 pins, marked 85, 87, etc.
  2. Connect the battery, turn the ignition on, listen for the pump to operate for 2 seconds. If no pump whine, proceed. If you hear the pump, and you didn’t before, hit the starter, see if it goes!!!

Replace the Fuel Pump:
  1. Disconnect the negative/ground cable from the battery
  2. Disconnect the filler & breather pipes (hoseclamps; flat head screw driver) from the rear of the tank, siphon out as much fuel as you can. Always have beer ready, if siphoning by mouth. I paid $5 for a siphon kit at O’Reilly. ...Worth it...
  3. Support the tank with blocks of some sort. I used jack stands with marginal success.
  4. Undo the two steel bands holding the tank on.
  5. Lower the tank about half way using a jack if you need. The tank will have to move rearward to clear the frame member at the front of the tank.
  6. Look at the code (i.e. “GFU”) on top of the pump. Call your favorite parts houses, and see if someone has one on the shelf, or get one ordered at this point (roughly $220). There are 2 kinds, and you can’t tell without the code on the pump.
  7. Use a flathead screwdriver and disconnect the 3-wire harness at the rear of the tank, and the 4-wire harness off of the pump in the middle of the tank. Use the pressure fitting disconnector tool (5/8th?) you rented to remove the fuel line couplings. You’re going to get gas everywhere. (BE CAREFUL!!! If you damage these lines, you can’t replace them; no one makes them. If you damage the inner retaining clips, like I did, Napa sells replacements for a couple bucks, but you’ll have to bring in the fuel line (disconnect at the fuel filter, and the supply line comes out easy) to show them what you need.)
  8. Take a breather, drink beer, do a sanity check here. The fuel pump harness should be a square harness with 4 wires. If it is a rectangle, your pump has already been replaced at least once, and your wires will be different colors except the grey wire. With a multi-meter, connect the leads to the grey wire in the fuel pump’s wiring harness and ground. Have the buddy who is drinking all your beer turn the ignition on. You should see 12 volts for about 2 seconds. If you don’t, your fuel pump isn’t getting power, and you’re chasing your tail. Try something else, but don’t continue here.
  9. Lower the tank to the ground
    Use a flathead screwdriver and hammer to turn the retaining ring, making sure as you loosen the ring, you push the little plastic catch the out of the way. You’ll see it. The pump is spring loaded, and will pop up a couple inches when free. Pull the old pump out.
  10. Your old pump will have a square harness. Your new pump will have a rectangular harness. Why? Because GM hates you. But this isn’t too bad. Drink more beer. The square harness, if you rub the dirt off of it, will have labels a, b, c, d on each wire. The new rectangular harness will have a & d on either end, it is alphabetical. Cut ‘A’ from the old harness, and splice it to ‘A’ on the new harness. The wire colors will not match up. The wire gauges will not match up. It will work anyway. Why? Because GM hates you. Splice the rest of your wires, drink more beer.
  11. Do another sanity check before you put the pump in gas, and void the return- connect the battery, connect the new harness to the new pump, (wash your hands) hold the pump, and have your buddy turn on the ignition. The new pump should roar for 2 seconds. If it doesn’t, you failed somewhere.
  12. Lube the new gasket with the new goop that came with the new pump, and install the new pump in the tank. You’ll have to push it down, and then get the retaining ring started again, and then hammer screwdriver the ring into place. This is a *****.
  13. Lift tank half way, and connect fuel line pressure fittings (no tools, just push them on), rear harness, pump harness, and front pipe.
  14. Lift tank all the way, attach the steel bands that hold the tank up, connect filler & breather pipes.
  15. Fill the tank with 5-ish gallons of gas and check for leaks from filler/breather
  16. Connect battery, turn ignition on, listen for 2 second pump operation, check for leaks
  17. Turn ignition off, listen for 2 second pump operation, check for leaks, then on again, listen for 2 second pump operation, check for leaks, turn ignition off, listen for 2 second pump operation, check for leaks.
  18. Pour a little beer on the ground in homage of GM’s recent bankruptcy, and start your truck.


Resident Cards Fan
Jul 31, 2009
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Phoenix, AZ
Anyone know if this write up applies to the NBS Tahoe's as well? If it does I would tackle this at some point to fix my fuel gauge issue.


Apr 17, 2010
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working on this now. having an issue with the "Pressure fitting disconnector tool" but working on it.

Broken Truck

Jul 11, 2010
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Near Boston
Good post. The Haynes manual really lead me wrong on this repair. I ended up jacking the truck up on all four corners and supporting each corner with 2 concrete blocks and a block of wood. You NEED the space! And like the posters says..... don;t buy the pump until you get the old one out. Look for the GFU or other code and then buy the pump. Careful touching the code. It can wipe off very easily.


Full Access Member
Aug 2, 2010
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I bought my tahoe a year and a half ago. The fuel pump was one of the first parts I needed to replace. GREAT write up. I wish I would have been apart of this forum when I went thru that...I did it in my driveway on jackstands.


TYF Newbie
Aug 27, 2010
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These are the basic steps and most tahoes are of similar part structures so it applies to all. It is indeed a good how to replace a fuel pump article, car repair noobs would find it easy to follow. a little more visuals would have been nice.
Last edited:


TYF Newbie
Oct 28, 2010
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Boulder, CO
Thanks for the writeup. It's hard to believe nobody sells a pump that just plugs into the harness. Time for a little research...

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