What you're replacing and why it matters
Your 1991 Chevy S-10 has two separate fuel system parts that filter and move gasoline to the engine: the fuel filter, which is a replaceable cartridge that catches debris, and the fuel pump, which is an electric motor inside the fuel tank that pressurizes the gas and pushes it through the fuel lines. The filter clogs over time and needs replacement every 15,000 to 30,000 miles depending on fuel quality and driving conditions. The pump fails less often but when it does, the truck won't start or will stall while running.
On your S-10, the fuel filter is mounted under the truck near the fuel tank—an easier job you can do yourself with basic tools. The fuel pump sits inside the tank and requires dropping the tank, which is more involved but still manageable in a driveway. Both jobs involve working with gasoline, so you need to follow safety steps carefully.
Key Takeaways
- The fuel filter on a 1991 S-10 is located under the truck and can be replaced without dropping the tank, using a wrench and a fuel line disconnect tool.
- The fuel pump is inside the tank and requires removing the fuel tank, disconnecting the pump module, and installing a new one—a longer job but doable without a lift.
- Both jobs require you to relieve fuel system pressure first by removing the fuel pump fuse and running the engine until it stalls.
- You will need a fuel filter cartridge, a fuel pump assembly (if replacing the pump), a fuel line disconnect tool, and basic wrenches; the filter costs $15 to $30 and the pump costs $80 to $150.
- Gasoline is flammable and produces fumes—work outdoors or in a well-ventilated space, keep sparks and flames away, and do not smoke.
Locating and replacing the fuel filter
The fuel filter on your S-10 is mounted horizontally under the truck, typically on the driver's side frame rail between the engine and the rear axle. You can see it from underneath without lifting the truck if you get low and look along the frame. It is a cylindrical metal canister about 4 inches long with fuel lines connected to both ends.
Before you touch anything, relieve the fuel system pressure. Locate the fuel pump fuse in the fuse box under the hood (your owner's manual shows the exact location and amperage). Pull the fuse out, then start the engine and let it run until it stalls—this empties the pressure in the lines. Turn off the ignition and wait a few minutes. Now you can safely disconnect the fuel lines without gasoline spraying out.
Slide under the truck and locate the filter. You will see two fuel lines connected to it—one coming from the tank and one going to the engine. Use a fuel line disconnect tool (a plastic clip tool that costs $5 to $10 at any auto parts store) to release each line by inserting the tool into the connector and gently pulling the line away. Have a small container or rag ready to catch any remaining fuel. Once both lines are free, use a wrench to unbolt the filter bracket from the frame—usually one or two bolts. Slide the old filter out and install the new one in the same position, bolt it down, and reconnect both fuel lines by pushing them firmly onto the new filter until you hear or feel a click.
Reinstall the fuel pump fuse, turn on the ignition (do not start the engine yet) and listen for a brief humming sound from the fuel pump—this means it is pressurizing the system. Start the engine and check under the truck for leaks around the filter connections. If you see fuel dripping, turn off the engine, wait a minute, and reseat the fuel lines by pushing them on more firmly.
Removing the fuel tank to access the pump
Replacing the fuel pump requires dropping the fuel tank, which means you need a safe way to support the truck. Use jack stands rated for your truck's weight—never rely on a jack alone. You will also need a fuel tank strap or support strap to lower the tank safely; a piece of sturdy rope or a ratchet strap works if you do not have the proper strap.
Start by relieving fuel system pressure the same way you did for the filter: pull the fuel pump fuse, run the engine until it stalls, and wait. Raise the rear of the truck on jack stands placed under the frame, not the bumper. Locate the fuel tank under the truck—it is a large metal or plastic container running across the width of the truck. You will see two metal straps bolted to the frame on either side of the tank holding it up.
Disconnect the fuel filler neck hose (the rubber hose that connects the filler cap opening to the tank) by loosening the hose clamp with a screwdriver. Disconnect the fuel lines at the top of the tank using your fuel line disconnect tool. You may also have an electrical connector for the fuel pump sending unit—unplug it by hand. Now unbolt the two tank straps using a wrench. Support the tank with your rope or strap looped through the frame, then slowly lower the tank by loosening the rope. Once it is low enough, you can slide it out from under the truck.
Removing and installing the fuel pump
Once the tank is out, you will see the fuel pump module bolted to the top of the tank. The module is a metal or plastic ring with the pump, filter, and sending unit all assembled together. Before you remove it, mark the orientation of the module with a marker or tape so you install the new one the same way—the fuel lines and electrical connector have a specific direction.
Use a fuel pump lock ring tool (a specialized wrench that costs $15 to $30) to unscrew the lock ring holding the pump module to the tank. If you do not have this tool, you can carefully use a hammer and a large screwdriver or punch to tap the ring counterclockwise, but the lock ring tool is safer and faster. Once the ring is loose, lift the pump module straight up and out of the tank. Disconnect the electrical connector and any fuel lines attached to the module.
Install the new pump module by reversing these steps: connect the electrical connector and any fuel lines to the new module, lower it into the tank opening with the orientation mark you made facing the same direction, and hand-tighten the lock ring. Use the lock ring tool to tighten it firmly—snug but not so hard you strip the threads. Do not overtighten.
Reinstalling the tank and reconnecting everything
Raise the fuel tank back under the truck using your rope or strap, aligning it so the bolt holes in the straps line up with the frame. Bolt both straps back down and tighten them evenly so the tank sits level. Reconnect the fuel filler neck hose and tighten the hose clamp. Reconnect the electrical connector for the fuel pump sending unit. Reconnect the fuel lines by pushing them firmly onto the tank fittings until they click.
Lower the truck off the jack stands carefully. Reinstall the fuel pump fuse. Turn on the ignition and listen for the fuel pump to hum for a few seconds—this means it is pressurizing the system. Start the engine and let it run for a minute, then turn it off and wait. Check under the truck for any fuel leaks around the tank connections, filler neck, and fuel lines. If you see dripping, turn the ignition off when ready, wait a few minutes, and check the connections again to make sure they are seated fully.
Tools and parts you will need
For a fuel filter replacement, you need a fuel line disconnect tool, a wrench set (usually 5/16-inch or 3/8-inch for the filter bracket bolts), a new fuel filter cartridge designed for a 1991 S-10, a small container or rag, and a fuel pump fuse (check your fuse box to confirm the amperage). The filter itself costs $15 to $30 depending on the brand.
For a fuel pump replacement, add a fuel tank strap or sturdy rope, a jack and jack stands rated for your truck's weight, a fuel pump lock ring tool, and a new fuel pump module assembly for a 1991 S-10 (costs $80 to $150). If you do not own a lock ring tool, you can rent one from an auto parts store for $5 to $10 or borrow one from a friend. Some stores will also remove and install the pump module for a fee if you bring them the tank.
Safety steps you cannot skip
Gasoline is highly flammable and produces vapors that can ignite from a spark or flame. Work outdoors or in a well-ventilated garage with the door open. Do not smoke, use a lighter, or create sparks near the fuel system. Wear safety glasses to protect your eyes from fuel spray when disconnecting lines. Keep a fire extinguisher rated for gasoline fires (Class B) nearby—do not use water on a gasoline fire.
Always relieve fuel system pressure before opening any fuel lines or removing the pump fuse. Never work on the fuel system with the engine running or hot—let the engine cool for at least 30 minutes after the last time you drove the truck. If you spill gasoline on your skin, wash it off when ready with soap and water. If you spill it on the ground, let it evaporate in open air and do not hose it down into storm drains.
Frequently Asked Questions
How do I know if my fuel pump is failing?
A failing pump usually causes the engine to stall while driving, hesitate when accelerating, or not start at all. You may also hear a whining noise from under the truck that gets louder as you drive. If the truck cranks but does not start and you have confirmed the fuel filter is clean and fuel is reaching the engine, the pump is likely bad.
Can I replace just the fuel pump filter inside the module instead of the whole pump?
On a 1991 S-10, the fuel pump module is sold as one complete assembly and is not designed to be disassembled in the field. Replacing the whole module is the standard approach. Some aftermarket modules may have a replaceable filter screen, but you would need to check the specific product documentation.
What if I cannot get the fuel lines disconnected?
Fuel line connectors can stick if they have not been disturbed in years. Spray the connector with penetrating oil and wait 15 minutes, then try the disconnect tool again. If it still will not budge, you can carefully cut the fuel line with a utility knife and install a new line with hose clamps, but this is messier and wastes the old line.
Do I need to drain the fuel tank before dropping it?
You do not have to completely empty it, but draining most of the fuel makes the tank lighter and safer to handle. Use a fuel siphon or a hand pump to remove fuel into a clean gas can. Leave just enough to keep the pump submerged so it does not run dry if you accidentally start the engine.
How long does a fuel pump usually last on a 1991 S-10?
Fuel pumps vary widely depending on fuel quality, driving habits, and how often the truck sits unused. Some last 100,000 miles or more; others fail at 60,000 miles. Running the tank very low frequently or using poor-quality fuel can shorten pump life because the pump uses gasoline to cool itself.