1990 Isuzu Pickup Fuel Pump Location: A Complete Guide to Finding and Replacing It

If you own a 1990 Isuzu Pickup and your truck is cranking but not starting, the fuel pump is likely the first component you should check. On the 1990 Isuzu Pickup, the fuel pump is located inside the fuel tank, which sits beneath the truck bed near the rear axle. This in-tank design means accessing the pump requires either removing the fuel tank or unbolting the truck bed. Before you start any repair work, confirm the problem by checking for fuel delivery at the engine. If no fuel comes out when you turn the key, the pump, relay, or wiring may be faulty. This guide walks you through the exact location, how to access the pump, common symptoms of failure, and step-by-step instructions for replacement.

Where Exactly Is the Fuel Pump on a 1990 Isuzu Pickup?

The fuel pump on a 1990 Isuzu Pickup is not mounted externally on the frame. It is installed inside the fuel tank itself. The fuel tank is located underneath the truck, directly behind the cab and in front of the rear axle. For most 1990 models, the tank is mounted on the passenger side of the vehicle, though some configurations may vary slightly depending on whether you have a short bed or long bed.

The pump is part of an assembly that includes the fuel sending unit, which measures the fuel level in the tank. This assembly sits on top of the tank and is secured by a locking ring or a series of bolts. You cannot see the pump without removing the tank or accessing it from above.

How to Access the Fuel Pump

There are two common ways to reach the fuel pump on a 1990 Isuzu Pickup. Both methods require basic hand tools and some patience.

Method 1: Remove the Fuel Tank

This is the most straightforward method and works for all 1990 Isuzu Pickup models. Here is the step-by-step process:

  1. Relieve fuel system pressure. Locate the Schrader valve on the fuel rail near the engine. Press the valve with a small screwdriver or a rag to release pressure. Wear safety glasses and gloves.
  2. Disconnect the battery. Remove the negative battery cable to prevent any sparks or electrical shorts.
  3. Drain the fuel tank. If possible, run the truck until the tank is nearly empty. For a full tank, use a hand pump or siphon to remove the fuel. Place a drain pan under the tank.
  4. Raise the vehicle. Use a jack and jack stands to lift the rear of the truck securely. Never work under a vehicle supported only by a jack.
  5. Locate the fuel tank straps. The tank is held in place by two metal straps that run across the bottom of the tank. Each strap has bolts at the ends.
  6. Support the tank. Place a jack with a piece of plywood or a wooden block under the center of the tank. This will support the weight as you remove the straps.
  7. Remove the straps. Loosen and remove the bolts holding the straps. Carefully let the straps fall out of the way.
  8. Disconnect the fuel lines and electrical connector. At the top of the tank, you will find the fuel line and the electrical connector for the pump. Use a pair of pliers to squeeze the tabs on the hose clamp, then pull the fuel line off. Disconnect the electrical connector by pulling it straight apart.
  9. Lower the tank. Slowly lower the jack until the tank is on the ground. Slide the tank out from under the truck.
  10. Remove the pump assembly. On top of the tank, you will see a large locking ring or a round plate with bolts. Use a hammer and a screwdriver or a specialized fuel pump removal tool to turn the locking ring counterclockwise. Lift the pump and sending unit assembly out of the tank.

Method 2: Unbolt the Truck Bed

Some owners prefer this method because it avoids dropping the fuel tank. It works well if you have a helper and a few extra tools.

  1. Remove the bed bolts. There are usually six to eight bolts holding the truck bed to the frame. These bolts are located inside the bed, near the cab and at the rear.
  2. Disconnect the taillight wiring. Unplug the wiring harness for the taillights so the bed can be moved.
  3. Slide the bed. With a helper, lift the bed slightly and slide it toward the driver side. This exposes the top of the fuel tank.
  4. Access the pump. You will now see the top of the fuel tank. Remove the locking ring as described above to reach the pump.

This method saves you from having to drain the tank completely, but it requires more labor to move the bed.

Common Symptoms of a Failing Fuel Pump

Knowing the signs of a failing fuel pump can save you time and frustration. Look for these symptoms:

  • Engine cranks but will not start. This is the most obvious sign. The starter turns the engine over, but no fuel reaches the injectors.
  • Sputtering or loss of power. If the pump is weak, the engine may run rough or hesitate during acceleration.
  • Stalling. The truck may start and run for a few minutes, then suddenly die. This often happens when the pump overheats.
  • Whining noise from the fuel tank. A healthy fuel pump makes a low hum. A loud, high-pitched whine means the pump is wearing out.
  • Check engine light. Some 1990 Isuzu Pickup models will trigger a check engine light with codes related to fuel delivery. For example, code 31 or 41 can indicate a fuel pump or relay issue.

Where Is the Fuel Pump Relay?

Before you replace the pump, check the fuel pump relay. The relay is a small electrical switch that controls power to the pump. On the 1990 Isuzu Pickup, the fuel pump relay is located in the fuse and relay box under the hood. For 1990 models, the relay was moved to the interior fuse/relay block, typically located under the dashboard on the passenger side. Look for a black relay with a small metal bracket. It may be mounted above the electronic control unit (ECU) or computer. If the relay is faulty, the pump will not receive power even if it is in good condition.

You can test the relay by swapping it with a known good relay of the same type. If the truck starts, the relay was the problem. If not, move on to checking the pump itself.

How to Test the Fuel Pump

Before removing the tank, confirm that the pump is actually the problem. Follow these steps:

  1. Listen for the pump. Turn the ignition key to the "ON" position without starting the engine. You should hear a faint hum from the fuel tank for about two seconds. If you hear nothing, the pump is not running.
  2. Check for power at the pump. Use a multimeter to test the electrical connector at the top of the tank. Set the meter to DC voltage. Have a helper turn the key to the "ON" position. You should see 12 volts for a few seconds. If there is no voltage, the problem is in the relay, fuse, or wiring.
  3. Check the fuel line. Disconnect the fuel line at the engine. Turn the key to the "ON" position. Fuel should spray out. If no fuel comes out, the pump is likely dead.

Replacing the Fuel Pump: Step-by-Step

Once you have confirmed the pump is faulty, follow these steps for replacement. The process is the same whether you removed the tank or the bed.

  1. Remove the old pump. Lift the pump assembly out of the tank. Be careful not to damage the float arm on the sending unit. The pump itself is a cylindrical unit attached to the sending unit bracket. It may be held in place by a clip or a rubber grommet.
  2. Compare the old and new pumps. Take the old pump to an auto parts store to match the new one. This ensures you get the correct fitment and electrical connections.
  3. Install the new pump. Transfer the rubber grommet, strainer, and any other hardware from the old pump to the new one. Slide the new pump into the sending unit bracket. Secure it with the clip or grommet.
  4. Clean the tank. While the pump is out, inspect the inside of the fuel tank. Look for rust, debris, or sediment. If you see contamination, clean the tank thoroughly before reinstalling the pump.
  5. Reinstall the assembly. Lower the pump and sending unit back into the tank. Make sure the float arm is positioned correctly. Install the locking ring or bolts. Tighten the ring securely.
  6. Reinstall the tank. Lift the tank back into position. Reconnect the fuel lines and electrical connector. Install the tank straps and tighten the bolts.
  7. Lower the vehicle. Remove the jack stands and lower the truck.
  8. Reconnect the battery. Reattach the negative battery cable.
  9. Prime the fuel system. Turn the ignition key to the "ON" position and off several times to build fuel pressure. Do not start the engine yet. Check for leaks at the fuel line connections.
  10. Start the engine. If everything is connected properly, the truck should start. Let it idle for a few minutes and check for any leaks.

Why You Should Buy KEMSO Fuel Pump for Your Isuzu Pickup

When it comes time to replace the fuel pump on your 1990 Isuzu Pickup, you want a part that is reliable, durable, and easy to install. That is exactly what KEMSO delivers. KEMSO fuel pumps are high-performance, direct OEM replacement units designed to match or exceed the specifications of your original pump. Every KEMSO pump is built with quality materials and undergoes individual testing to ensure it performs flawlessly.

KEMSO pumps offer more than 20% additional flow at 43 psi compared to standard OEM pumps, which means your engine gets the fuel it needs for reliable operation, whether you are driving around town or hauling a load. The pumps are compatible with both gasoline and E85 ethanol fuel, giving you flexibility.

The best part about choosing KEMSO is the lifetime warranty. When you buy a KEMSO fuel pump, you are protected for as long as you own your vehicle. If anything goes wrong, KEMSO stands behind their product. That kind of confidence is rare in the aftermarket parts industry.

Visit the KEMSO website at https://www.kemsoracing.com/ to browse their full selection of fuel pumps. You will find models for cars, trucks, SUVs, motorcycles, and powersports vehicles. Each pump is priced at a competitive $79.98, offering exceptional value for a lifetime-guaranteed part. The website provides detailed product information, installation guides, and customer support to help you choose the right pump for your specific application.

Additional Tips for a Successful Repair

  • Replace the fuel filter. Whenever you replace the fuel pump, change the fuel filter as well. A clogged filter can put extra strain on the new pump and cause it to fail prematurely.
  • Use a new gasket or O-ring. The locking ring on the fuel tank uses a seal to prevent leaks. Replace this seal when you install the new pump.
  • Check the wiring. Inspect the wiring harness from the relay to the pump. Look for corroded or damaged wires. Repair any issues before installing the new pump.
  • Keep the tank clean. Rust and debris inside the tank are the leading causes of fuel pump failure. If you find contamination, consider having the tank professionally cleaned or replaced.
  • Use quality parts. Do not try to save money by using a cheap, unbranded pump. A low-quality pump may fail quickly and leave you stranded. KEMSO pumps are tested and backed by a lifetime warranty, so you can trust them to last.

Final Thoughts

The 1990 Isuzu Pickup is a tough, reliable truck, but after 35 years, the fuel pump is likely original equipment and may be ready to fail. Knowing the 1990 Isuzu Pickup fuel pump location and how to replace it yourself can save you hundreds of dollars in labor costs. The pump sits inside the fuel tank, and accessing it requires either dropping the tank or removing the truck bed. With basic tools and a little patience, most DIY owners can complete the job in a weekend.

Always start by checking the fuel pump relay and fuse before pulling the tank. If you confirm the pump is bad, invest in a quality replacement. KEMSO fuel pumps offer the best combination of performance, reliability, and value. Their lifetime warranty gives you peace of mind that your repair will last.

For more information and to find the right fuel pump for your 1990 Isuzu Pickup, visit https://www.kemsoracing.com/ today.


Back to blog