Introduction

Upgrading the fuel pump on your SW20 Turbo is one of the most important steps to support higher horsepower and ensure reliable fuel delivery under heavy load. The Walbro 255lph fuel pump has become the go-to choice for MR2 Turbo enthusiasts because it offers a proven flow rate upgrade compared to the factory pump without requiring major modifications. This guide provides a detailed, step-by-step walkthrough for installing the Walbro 255lph pump in your SW20 Turbo, along with critical electrical and safety considerations that many shorter guides skip.

A stock SW20 Turbo fuel pump flows approximately 100 liters per hour at 40 psi of fuel pressure. When you add a boost controller, larger injectors, or a standalone ECU, that stock pump quickly becomes a bottleneck. The Walbro 255lph pump provides roughly 2.5 times the flow at the same pressure, giving you headroom for up to 500 horsepower on pump gas. Installing it correctly ensures you get that performance without risking fuel starvation or voltage drop issues.

Tools and Materials Needed

Before starting, gather all necessary tools and parts. Using a dedicated installation kit saves time and prevents leaks from reused O-rings or incorrect fittings.

  • Walbro 255lph fuel pump (part number F20000171 for the direct-fit SW20 kit or GSS341 for a universal inline pump)
  • Fuel pump installation kit – includes new rubber hose, O-rings, hose clamps, and a strainer sock
  • Flathead and Phillips screwdrivers
  • 10mm and 12mm sockets with ratchet and extensions
  • Jack and jack stands or ramps
  • Safety glasses and nitrile gloves
  • Fuel line clamp pliers (for pinching rubber lines without damage)
  • Electrical tape, heat shrink tubing, and a wire stripper/crimper
  • Digital multimeter (to verify voltage at the pump)
  • Shop rags for any fuel spills
  • Fire extinguisher rated for gasoline (always nearby)

If your car is an early SW20 (1990–1992), the fuel pump assembly uses a slightly different retaining ring design. Aftermarket installation kits often include adapters. Check your kit contents against the year of your MR2 before beginning.

Preparation Steps

Proper preparation prevents accidents and wasted time. Follow these steps exactly, and do not skip the fuel pressure relief procedure.

Relieve Fuel System Pressure

  • Park the car on level ground and set the parking brake.
  • Locate the fuel pump fuse in the under‑hood fuse box (marked FUEL PUMP or F/P). Remove it carefully.
  • Start the engine and let it idle until it stalls from fuel starvation. Turn the key off.
  • Turn the ignition key to the ON position (do not start) for 3 seconds to confirm the pump does not run.
  • Reinstall the fuel pump fuse after the engine stalls. This steps releases residual pressure in the lines.

Even after stalling, a small amount of fuel may still be under pressure. Wear safety glasses and have rags ready when disconnecting lines.

Disconnect the Battery

Remove the negative terminal cable from the battery and secure it away from the terminal. This eliminates any risk of sparks while working near fuel vapors and also protects the ECU during electrical work.

Ventilation and Fire Safety

Gasoline vapors are heavier than air and can pool near the floor. Work in a well‑ventilated garage with the door open, or better yet outdoors. Keep the fire extinguisher within arm’s reach. Do not operate any power tools that create sparks near the fuel tank area.

Removing the Old Fuel Pump

The SW20 Turbo fuel pump is located inside the fuel tank, accessed through a panel in the trunk. The process is straightforward but requires patience.

Access the Fuel Pump Cover

  • Open the trunk and remove the carpeted floor liner. You will see a black metal plate about 6 inches in diameter held by four 10mm bolts.
  • Remove the bolts and lift off the cover plate. The fuel pump assembly sits directly underneath.
  • Carefully disconnect the electrical connector on top of the assembly by pressing the locking tab.
  • Disconnect the fuel supply line (usually a quick‑connect fitting). Press the two tabs on the sides of the fitting and pull straight up. Some fuel may drip – use rags.
  • Disconnect the fuel return line (smaller diameter) using the same method.

Remove the Pump Bracket and Pump

  • Turn the large plastic retaining ring counter‑clockwise using a flathead screwdriver and a rubber mallet. It is tight – do not force it; tap gently around the edges.
  • Lift the entire bracket assembly out of the tank. The bracket holds the pump, a foam sleeve, and the fuel sender unit.
  • Place the assembly on a clean cloth to avoid scratching the surfaces.
  • Remove the rubber hose and clamps connecting the bottom of the pump to the bracket outlet.
  • Unclip the electrical leads from the pump housing. Note the polarity: black is ground (negative), red/white is positive.
  • Slide the pump out of its rubber isolation sleeve. The old sock filter may stay attached – remove it carefully.

Inspect the tank interior for sediment or rust. If you see debris, consider replacing the fuel filter (located under the car near the firewall) before installing the new pump. A contaminated filter can restrict flow and ruin your new pump.

Installing the Walbro 255lph Fuel Pump

Now install the Walbro pump using fresh hardware from the installation kit.

Assemble the New Pump into the Bracket

  • Slide the new Walbro pump into the rubber isolation sleeve. Make sure the pump orientation matches the old one: the electrical terminals should be pointing upward and aligned with the bracket cutout.
  • Attach the new sock strainer to the bottom of the pump. Press it on until it clicks. Do not reuse the old one – it can collapse under the higher flow.
  • Connect the length of submersible fuel hose (supplied in most kits) from the pump outlet to the bracket outlet. Use two hose clamps per connection, one near each end, and tighten firmly.
  • Reattach the electrical connectors. Crimp them securely or solder them – many Walbro pump failures trace back to poor electrical connection. Use heat shrink tubing to insulate each joint.
  • Insert the assembly back into the fuel tank. Make sure the fuel level float arm is not bent and swings freely.
  • Press the plastic retaining ring down and turn it clockwise until it clicks. Torque it snug – hand tight plus a quarter turn is enough.

Reconnect Fuel Lines and Wiring

  • Reattach the fuel supply line quick‑connect fitting – push it down until you hear a snap. Pull gently to confirm it is locked.
  • Reattach the return line fitting similarly.
  • Plug the main electrical connector back into the top of the assembly.
  • Replace the metal access cover plate and tighten its bolts to 7–9 ft-lb (do not overtighten, the threads are soft).

Electrical Wiring Upgrades

The Walbro 255lph pump draws more current than the stock pump – about 8–10 amps at 13.5V under load, versus the stock pump’s 5–6 amps. The factory wiring, especially the ground circuit, may not deliver consistent voltage. Voltage drop causes the pump to flow less than its rating, defeating the purpose of the upgrade.

Voltage Drop Check

  • With the battery reconnected and the fuse installed, turn the key ON and listen for the pump to prime (2 seconds).
  • Using a multimeter set to DC volts, probe the positive and negative wires at the pump connector while the pump is running. You should see at least 13.0V at the pump. If it is below 12.5V, the wiring needs upgrading.

Relay and Wire Upgrade Option

Many owners run a dedicated 12‑gauge supply wire from the battery, through a 20‑amp inline fuse, to a 40‑amp relay triggered by the factory fuel pump signal. This ensures full voltage to the pump. A good ground on the chassis near the tank is equally important. Detailed wiring mod tutorials are available on MR2OC forums. We recommend performing this mod at the same time as the pump install to avoid having to pull the pump out again.

Testing the Installation

After completing the wiring and reconnecting the battery, test the system before reinstalling the trunk interior.

Prime and Leak Check

  • Turn the ignition to ON (position II) without starting the engine. You should hear a brief hum from the fuel pump for 2–3 seconds.
  • Listen for any sputtering or abnormal whining. A healthy Walbro pump makes a low pitched hum; a high‑pitched shriek may indicate cavitation (air in the fuel) or a pinched hose.
  • Check all fuel line connections and the access cover plate for any fuel seepage. Use a clean paper towel to wipe around each joint and then inspect after 1 minute.
  • If no leaks are present, start the engine. Let it idle for 2 minutes while visually inspecting again.
  • Take the car for a short spin – 5 minutes at varying speeds – then check the trunk area for any fuel smells or drips.

Fuel Pressure Verification

Ideally, you should measure fuel pressure at the fuel rail. The Walbro 255lph with the factory fuel pressure regulator will maintain a baseline of 35–38 psi (vacuum line connected) and 40–44 psi (vacuum disconnected). If pressure is significantly lower, check for a clogged fuel filter or loose hose inside the tank. Racetronix fuel pressure specs provide a good reference for 255lph pumps.

Performance Tuning Considerations

Installing the Walbro pump is often part of a larger upgrade path. Consider these companion modifications to maximize its benefit.

Fuel Pressure Regulator

If you are running more than 15 psi of boost or have aftermarket injectors, an adjustable fuel pressure regulator (AFPR) lets you precisely set the base pressure. The Walbro 255lph can supply enough volume to maintain higher base pressures (up to 50 psi) without starving the injectors.

Injector Upgrade

The stock 440 cc/min injectors will run out of flow around 350 wheel horsepower. Pairing the Walbro pump with 550cc or 660cc injectors is a common combination for a reliable 400+ WHP setup. Be sure to get the injectors flow‑matched and tune the ECU accordingly.

Fuel Filter Replacement

The fuel filter on the SW20 Turbo is located on the firewall, driver’s side. Replace it at the same time as the pump. A clogged filter can restrict flow enough to cause fuel pressure drop and lean the air‑fuel mixture. Use a high‑filtration unit like the Fensport WIX 33348.

Fuel Lines and Hoses

Rubber fuel lines inside the engine bay can degrade over time, especially if you are running E85. The Walbro 255lph pump works well with ethanol blends, but old rubber hoses may swell or leak. Replace them with ethanol‑rated PTFE or high‑pressure rubber lines for long‑term reliability.

Final Steps

  • Reinstall the trunk carpet and liner and any trim pieces you removed.
  • Dispose of the old pump, fuel sock, and oily rags according to local hazardous waste regulations.
  • Reset your ECU by disconnecting the battery for 10 minutes (if you have not already) to clear any fuel trim adaptations from the old pump.
  • Take a final test drive that includes moderate acceleration, full‑throttle pulls, and steady‑speed cruising. Listen for any changes in fuel pump noise – a constant hum is normal; a rattling sound may mean the pump is not fully seated in the isolation sleeve.
  • Check your fuel pressure gauge if you have one installed to confirm the pump holds pressure after shutdown. The system should retain residual pressure for several minutes.

Conclusion

Installing a Walbro 255lph fuel pump in your SW20 Turbo is one of the most cost‑effective upgrades you can perform to ensure safe fuel delivery for increased power. By following the detailed steps in this guide, you can confidently complete the installation, address common voltage and wiring issues, and integrate the pump into a larger fuel system upgrade. With proper installation and flow‑matched supporting modifications, the Walbro 255lph will support your MR2 Turbo reliably for years of hard driving.

For further reading, visit the official Walbro 255lph pump specifications page or consult the SW20 Turbo factory service manual for torque specifications and wiring diagrams.