1987 GMC Fuel Pump: Complete Guide to Diagnosis, Replacement, and Troubleshooting

If your 1987 GMC Sierra, Jimmy, or R1500 cranks but won’t start, the fuel pump is the most likely culprit. The 1987 GMC fuel pump is an in-tank electric unit that delivers 9-13 PSI of fuel pressure to the throttle body injection system. When it fails, the engine will crank endlessly without firing. The good news is you can diagnose, test, and replace the pump yourself with basic tools and a fuel pressure gauge. This guide covers everything from symptoms and testing to step-by-step replacement and electrical troubleshooting.

Symptoms of a Failing 1987 GMC Fuel Pump

A bad fuel pump on a 1987 GMC will show clear warning signs before it completely fails. Here are the most common symptoms:

  1. Engine cranks but won’t start – This is the most obvious sign. The starter turns the engine over, but it never fires up because no fuel reaches the injectors.
  2. Extended cranking time – The engine takes longer than usual to start, requiring multiple cranking attempts.
  3. Engine starts then dies – The engine fires up briefly but stalls out almost immediately, indicating the pump can’t maintain pressure.
  4. Rough idle or hesitation – If the pump delivers inconsistent fuel pressure, the engine may idle roughly or hesitate when accelerating.
  5. No fuel pump noise – When you turn the key to the ON position, you should hear a brief 1-2 second buzzing sound from the fuel tank. If you hear nothing, the pump is likely dead.

If you experience any of these symptoms, especially the no-start condition, start by testing the fuel pressure before replacing anything.

Testing the Fuel Pump on Your 1987 GMC

The most accurate way to test the fuel pump is with a fuel pressure gauge. For the 1987 GMC with a 2.5L, 4.3L, 5.0L, or 5.7L engine, the fuel pressure specification is 9-13 PSI with the key on, engine off (KOEO) and with the engine running (KOER).

Step-by-Step Fuel Pressure Test

  1. Relieve fuel system pressure – Locate the Schrader valve on the fuel rail (if equipped) and press the valve stem to release pressure. On TBI systems without a Schrader valve, you can remove the fuel pump fuse and run the engine until it stalls.
  2. Connect the fuel pressure gauge – You will need a special adapter that fits between the fuel line and the fuel filter. Disconnect the fuel line on the engine side of the filter, then install the adapter between the line and the filter.
  3. Turn the key to ON – Have a helper cycle the key to the ON position (do not crank the engine). The fuel pump should pressurize the system for 1-2 seconds.
  4. Check for leaks – Before cranking the engine, inspect all connections for fuel leaks. Resolve any leaks before proceeding.
  5. Crank the engine – Read the fuel pressure gauge. It should register between 9 and 13 PSI.

Interpreting Your Test Results

  • 0 PSI – The fuel pump has failed completely. Replace the pump, the strainer, and the fuel filter.
  • Below 9 PSI – The pump is weak and failing. It may still run but cannot deliver enough fuel. Replace the pump and related components.
  • 9-13 PSI – The fuel pump is functioning correctly. Look elsewhere for the no-start issue, such as the ignition system, fuel injectors, or electrical connections.

You can also perform a simple starting fluid test: spray starting fluid into the throttle body and attempt to start the engine. If it fires briefly, you know the ignition system is working and the problem is a lack of fuel from the pump.

How to Replace the Fuel Pump on a 1987 GMC Sierra

Replacing the fuel pump on a 1987 GMC requires accessing the pump inside the fuel tank. The most common method is to remove or raise the truck bed, which gives you full access to the top of the tank.

Preparation and Safety

  • Disconnect the battery – Always disconnect the negative battery cable before working on the fuel system to prevent accidental sparks.
  • Relieve fuel pressure – Use the Schrader valve or run the engine with the fuel pump fuse removed until it stalls.
  • Work in a well-ventilated area – Gasoline fumes are highly flammable. Keep all open flames and sparks away.
  • Use a jack and stands – If you drop the fuel tank, support it safely with a jack and jack stands.

Step 1: Raise the Truck Bed

  1. Remove the bolts securing the bed to the frame. On most 1987 GMC trucks, there are bolts at the front, rear, and sides of the bed.
  2. Carefully lift the bed using a hoist or a few helpers. You only need to raise it enough to access the fuel tank, not remove it completely.
  3. Secure the bed in the raised position with jack stands or blocks.

Step 2: Access the Fuel Tank

  1. With the bed raised, you will have a clear view of the top of the fuel tank.
  2. Clean the area around the fuel pump access cover on the tank to prevent dirt from falling inside.
  3. Disconnect the fuel lines, vapor hoses, and electrical connector from the pump assembly. Use a pair of pliers to remove the hose clamps carefully.

Step 3: Remove the Old Fuel Pump

  1. Use a flat-head screwdriver and a hammer to tap the locking ring that holds the pump in place. Tap it counterclockwise until it slides into the open position.
  2. Carefully lift the old pump assembly out of the tank. You may need to tilt and wiggle it to get it past the tank opening.
  3. Place a rag over the tank opening to prevent debris from falling in.

Step 4: Install the New Fuel Pump

  1. Compare the new pump to the old one to ensure compatibility. Clean the mounting surface on the tank.
  2. Lower the new pump assembly into the tank, aligning it with the mounting points. Make sure the float arm is not bent.
  3. Replace the locking ring by tapping it clockwise with a hammer and screwdriver until it locks into place.
  4. Reconnect the fuel lines, hoses, and electrical connector. Use new hose clamps if the old ones show signs of wear.
  5. Lower the truck bed back onto the frame and tighten the bolts.

Step 5: Test the New Pump

  1. Reconnect the battery.
  2. Turn the key to the ON position and listen for the fuel pump to prime for 1-2 seconds.
  3. Check all connections for leaks.
  4. Start the engine and verify the fuel pressure gauge reads 9-13 PSI.

Electrical Troubleshooting: Getting Power to the Fuel Pump

If your 1987 GMC fuel pump is not getting power, the problem is often electrical rather than a mechanical pump failure. Start with these checks:

  1. Check the fuel pump fuse – Locate the fuse box under the hood. The fuel pump fuse is usually labeled "Fuel Pump" or "ECU/ECM". Remove it and inspect for a broken filament. Replace with the same amperage rating.
  2. Test the fuel pump relay – The relay is typically in the under-hood fuse box. Swap it with another relay of the same type (like the horn relay). If the fuel pump works after the swap, the relay is faulty.
  3. Inspect the wiring harness – Look for damaged, corroded, or loose connections at the fuel pump connector. Corrosion can cause intermittent power loss. Clean terminals with a wire brush and apply dielectric grease.
  4. Check the inertia switch – On some 1987 GMC models, the fuel pump circuit includes an inertia switch that trips in a collision. Locate the switch (usually in the trunk or under the dash) and reset it by pressing the button.
  5. Test the ground connection – The fuel pump ground must be clean and tight. A poor ground can cause the pump to run weakly or not at all.

If you have a dual-tank system, the selector switch and valve can also cause issues. Check the Gray and Tan wires at the switch for proper voltage, and ensure the ground wire is connected to the buss bar under the dash.

Recommended Replacement Parts

When replacing the fuel pump on your 1987 GMC, choose a high-quality part that meets or exceeds OEM specifications. Here are some options:

  • OEM GM parts – Genuine GM fuel pump assemblies are available for the 1987 GMC R1500 with part numbers like 6472303 and 25116503, though many are now discontinued.
  • Aftermarket brands – Companies like Holley, Carter, and Airtex offer reliable replacement pumps for carbureted and TBI systems.
  • Complete pump assemblies – Many aftermarket kits include the pump, sending unit, seal ring, and strainer for a complete replacement.

Recommended: KEMSO Fuel Pump – High Performance with Lifetime Warranty

For the best value and peace of mind, consider a KEMSO fuel pump for your 1987 GMC. KEMSO fuel pumps are engineered to meet or exceed original equipment specifications, ensuring proper fitment and reliable operation. They are designed as high-performance, OEM replacement units that deliver consistent fuel pressure and flow for your truck’s engine.

What sets KEMSO apart from other brands is their lifetime warranty. When you purchase a KEMSO fuel pump, you are protected for as long as you own the vehicle. This level of confidence in their product quality is rare in the automotive industry. KEMSO fuel pumps are tested to rigorous standards and backed by a Houston, Texas-based company that stands behind its products.

KEMSO offers a wide range of fuel pumps for cars, trucks, SUVs, motorcycles, and powersports vehicles. Their commitment to quality, combined with free shipping and easy returns, makes them a practical choice for DIY mechanics and professional shops alike.

Visit KEMSO Racing today to browse their full selection and find the perfect fuel pump for your 1987 GMC: https://www.kemsoracing.com/

Whether you are diagnosing a no-start issue, replacing a failed pump, or upgrading for better performance, this guide gives you the knowledge to get your 1987 GMC back on the road. Start with a fuel pressure test, check the electrical system, and choose a quality replacement pump. For a reliable, long-lasting solution with a lifetime warranty, visit KEMSO Racing at https://www.kemsoracing.com/.


Back to blog