1. Preparation:
* Safety First: Disconnect the negative battery terminal. Work in a well-ventilated area. Fuel is flammable and fumes can be dangerous.
* Gather Tools: You'll need a socket set (including metric and standard), wrenches, screwdrivers (Phillips and flathead), fuel line disconnect tools, a fuel pump removal tool (often a specialized tool or a strong pry bar), safety glasses, gloves, rags, jack stands, and possibly a fuel pressure gauge.
* Drain the Fuel Tank (Highly Recommended): This significantly reduces the risk of fuel spills. Use a siphon pump to safely remove most of the fuel.
2. Accessing the Fuel Pump:
* Lower the Fuel Tank (Usually Required): This is the most challenging part. You'll likely need to:
* Support the truck securely with jack stands.
* Locate the fuel tank straps and their fasteners (usually bolts).
* Carefully lower the fuel tank. This often involves disconnecting fuel lines, the fuel level sender, and possibly the tank breather hose.
* Alternative Access (Some Models): Some 1990 Sierras *might* have access through a hatch in the bed of the truck, under the rear seat, or from underneath the vehicle, but this is less common. Check your repair manual.
3. Removing the Fuel Pump:
* Disconnect the Electrical Connector: Carefully disconnect the electrical connector from the fuel pump.
* Disconnect Fuel Lines: Use fuel line disconnect tools to carefully separate the fuel lines from the fuel pump. Have rags ready to absorb any spilled fuel.
* Remove the Fuel Pump Access Cover: This is usually a circular cover held in place by bolts or clips.
* Remove the Fuel Pump: Use the specialized fuel pump removal tool to carefully remove the pump assembly from the tank. If you don't have the tool, you might need to be very careful using a pry bar – avoid damaging the fuel tank's plastic sending unit.
4. Installing the New Fuel Pump:
* Install the New Fuel Pump: Carefully install the new fuel pump, ensuring it seats properly.
* Reconnect Fuel Lines: Carefully reconnect the fuel lines, ensuring tight seals.
* Reconnect Electrical Connector: Reconnect the electrical connector to the fuel pump.
* Reinstall the Fuel Pump Access Cover: Securely reinstall the fuel pump access cover.
5. Reassembly:
* Raise the Fuel Tank: Carefully raise the fuel tank back into its position.
* Reconnect Fuel Tank Straps: Securely reattach the fuel tank straps.
* Reconnect Fuel Lines, Sender, and Breather Hose: Make sure all connections are secure.
* Reconnect the Battery: Reconnect the negative battery terminal.
6. Post-Installation:
* Check for Leaks: Inspect all fuel line connections for leaks.
* Start the Engine: Start the engine and check for any problems. Listen for unusual noises from the fuel pump.
* Verify Fuel Pressure (Optional but Recommended): Use a fuel pressure gauge to verify proper fuel pressure.
Important Notes:
* Repair Manual: A repair manual specific to your vehicle is essential. It will provide detailed instructions, torque specifications, and diagrams specific to your truck's model.
* Safety: Work in a well-ventilated area. Fuel is flammable and potentially explosive.
* Professional Help: If you are not comfortable performing this repair yourself, take your vehicle to a qualified mechanic.
This is a complex repair. Incorrect installation can lead to fuel leaks, engine damage, or even fire. If you're unsure about any step, it's best to seek professional assistance. Remember to always prioritize safety.
