The fuel pump in a 1991 GMC Sierra truck is in the fuel tank. When the fuel pump goes out, the fuel tank has to be pulled down to get the pump out of the tank. A new fuel pump will include an O-ring, the pump and a strainer. Replace these parts as the fuel pump assembly is pulled out of the tank. The fuel filter should also be replaced to give the whole fuel system a tune-up.
Park your Sierra on a level surface and set the parking brake.
Locate the fuel tank in the back of the Sierra. Place a jack under the tank. Raise the jack to the bottom of the tank. This will help to bring the tank down when the straps are removed.
Unbolt the two straps holding the fuel tank in place with a socket wrench. There is a bolt on each end of the two straps. Lower the fuel tank onto the jack. Do not lower the tank until all the wires and hoses are disconnected.
Access the electrical connector at the top of the fuel tank. Raise the locking tab and pull the connectors apart. Pull the vacuum hoses off the lines by hand. Disconnect the fuel lines from the top of the fuel tank. The fuel lines will have a quick-disconnect fitting. Squeeze the fitting and pull off the fuel line.
Unscrew the hose clamp on the fuel filler pipe at the back of the fuel tank with a flat-head screwdriver. Pull the hose off the tank.
Lower the tank to the ground. Pull the tank off the jack and out from under the Sierra.
Unscrew the retaining ring at the top of the tank with a flat-head screwdriver and a hammer. The screwdriver will act as a punch. Strike the end of the screwdriver with the hammer in a counterclockwise motion . Once the retaining ring is loose, pull off the fuel tank.
Pull the O-ring off the threads and replace with a new O-ring. This will prevent leaking when the fuel tank is filled up.
Lift the fuel pump out of the tank. Pull it out at an angle, as the sending unit will obstruct it from coming out straight.
Pull the cylinder-shaped fuel pump off the assembly. Disconnect the electrical wire at the top of the pump. Replace with the new pump. The pump will clip into place. Screw the strainer into the bottom of the pump. The strainer will bolt into place. Connect the wiring harness to the top of the pump.
Insert the fuel pump assembly into the fuel tank. Place it at an angle so the sending unit does not get bent.
Thread the retaining ring by hand. Tighten the ring by pushing it with the screwdriver and hammer.
Place the fuel tank on the jack. Slide under the truck. Raise the fuel tank high enough to connect all the wiring and hoses, which will lock in place once they are attached to their respective connections.
Slide the fuel filler hose onto the back of the fuel tank. Slide the hose clamp over the hose and the piping. Tighten the hose clamp with a flat-head screwdriver.
Raise the tank the rest of the way to its mounting position. Bolt the two straps by hand to ensure that all four bolts are started correctly. Tighten the bolts with a socket wrench.
Pull the jack and the tools out from under the truck.
Add fuel to the tank.
Turn the ignition key to the "Start" position. The fuel pump will run for three seconds and shut off. This will prime the fuel system.
Start the Sierra and allow it to idle for five minutes. Inspect the fuel tank for leaks while the truck is running. Turn the engine off.
