Why Upgrade to a Walbro 255 Fuel Pump?

Your Subaru WRX’s stock fuel pump is designed for factory power levels. Once you add a bigger turbo, larger injectors, or an aftermarket engine management system, the stock pump often can’t keep up with increased fuel demand. A Walbro 255 LPH (liters per hour) fuel pump delivers a 40–60% flow increase over the stock unit, ensuring consistent fuel pressure under wide-open throttle. This upgrade is a prerequisite for safely running ethanol blends (E85) or boosting beyond 300–350 whp on a GD/GG chassis, and it remains a popular choice for both GR and VA models making up to 450 whp.

The Walbro 255 is a direct drop-in replacement for most Subaru fuel pump assemblies. The kit includes the pump, a new strainer sock, and sometimes an installation grommet. Although the installation is straightforward, skipping steps or rushing the fuel line disconnection can lead to leaks or damaged components. This guide covers every nuance—from relieving system pressure to verifying the final fuel pressure.

Tools and Materials

Before touching any fasteners, lay out everything you need. Working on the fuel system means you want to minimize time with the fuel tank open to reduce vapor exposure and contamination risk.

Required Tools

  • Walbro 255 fuel pump kit – Part number F20000169 (standard) or F20000180 (E85 compatible). Verify compatibility with your WRX model year (GD 2002–2007, GR 2008–2014, VA 2015–2021).
  • 10 mm, 12 mm, 14 mm sockets and wrenches – For seat bolts, access panel, and battery terminal.
  • Phillips and flathead screwdrivers – For plastic panel clips and the fuel pump locking ring (some models use a flathead for the ring).
  • Fuel line disconnect tool – 5/16″ or 8 mm plastic clip tool. Do not use a metal pick unless you are replacing the line.
  • Needle-nose pliers – For hose clamps and small clips.
  • Pick set or small pry bar – To release the fuel pump assembly from the tank.
  • Safety glasses and nitrile gloves – Fuel vapors and liquid are hazardous.
  • Fire extinguisher (Class B) – Keep within arm’s reach.
  • Clean rags and a small catch pan – For residual fuel.
  • New fuel filter – While you have the system open, replace the inline or in-tank filter (varies by year). A clogged filter will negate the flow improvements.
  • Torque wrench (in-lb) – For the fuel pump retaining ring (typically 20–30 in-lb, but verify).
  • Multimeter or fuel pressure gauge – To test pump voltage and fuel pressure after installation.
  • Rubbing alcohol or contact cleaner – To clean any fuel residue off electrical connectors.

Preparation and Safety

Fuel system work requires a well-ventilated workspace. No smoking, no open flames, and no cell phone use near the work area. Disconnect the battery negative terminal and wait at least 5 minutes before proceeding—this ensures the airbag capacitor drains and prevents any spark.

Relieving Fuel System Pressure

Subaru’s fuel system holds pressure even after the engine is off. Failing to relieve it can result in a high-pressure spray of fuel when you disconnect a line. Follow these steps:

  1. Remove the fuel pump fuse from the interior fuse box (driver’s footwell). On a GD/GG WRX, it’s fuse #11 (15A). On a VA WRX, consult your manual—the fuse is often labeled “FUEL PUMP” or “F/P.”
  2. Start the engine and let it idle until it stalls (usually 10–30 seconds).
  3. Crank the engine for 3–5 seconds to confirm no starting pressure remains.
  4. Turn the ignition off and reinstall the fuse (you’ll need it later for priming).

Now open the fuel filler cap to vent any remaining tank vapor. This step is often overlooked but prevents a vacuum lock when you lift the pump assembly.

Interior Access

For all WRX generations, the fuel pump is accessed from inside the cabin under the rear seat. Remove the lower seat cushion by pushing it rearward and lifting up at the front. Some models have a single bolt in the center (10 mm); others use push-clips. Once the cushion is out, you’ll see a metal access plate with four 10 mm bolts or two Phillips screws. Remove the plate to reveal the top of the fuel pump assembly. Lay a rag around the opening to catch any drips.

Removing the Stock Fuel Pump

You are now looking at the circular black fuel pump module. Before doing anything, clean the area with a damp rag to prevent dirt from falling into the tank. Dirt will destroy a high-pressure pump in seconds.

Disconnecting Fuel Lines and Wire Harness

  1. Identify the fuel lines. Typically there are two: a large supply line (5/16″ or 8 mm) and a smaller return line (some models combine the return into the module). Take a photo with your phone for reference.
  2. Use the plastic disconnect tool. Slide it between the line and the fitting. Push the tool inward while pulling the line outward. A small amount of residual fuel will spill; have a rag ready.
  3. Unplug the electrical connector. It has a locking tab; press the tab and pull straight up. Do not pry on the connector housing.
  4. Remove the retaining ring. This is a large plastic or metal ring that screws down to hold the pump module in the tank. Use a socket, wrench, or flathead screwdriver on the notches. Turn counterclockwise. It may be tight—apply steady pressure. Once loose, unscrew by hand.
  5. Lift the assembly. Grasp the top of the module and lift straight up. It may stick due to the tank seal gasket. Rotate the assembly slightly to release it. Place the module on a clean surface—do not set it directly on the ground.

Drain any fuel from the module into the catch pan. Note the orientation of the rubber seal on the tank opening; if it’s damaged, replace it.

Installing the Walbro 255

The Walbro 255 pump is longer than the stock unit on many WRX models. You must transfer the existing pump brackets, insulators, and wiring from the old pump to the new one. The pump itself is mounted inside the plastic module.

Disassembling the Module

  1. Remove the large rubber or plastic grommet that holds the pump body. Some models use a clip; others press-fit.
  2. Slide the old pump out of the bottom bracket. Note the direction of flow—the outlet nozzle usually points up.
  3. Remove the old strainer sock from the bottom of the pump (it may have a snap ring or push-fit). Discard it.

Prepping the Walbro Pump

  • Install the new strainer sock that comes with the Walbro kit onto the bottom of the pump. Ensure it clicks or fits snugly. The sock orientation ensures proper pickup; the open end must face the bottom of the tank.
  • Slide the pump into the module’s lower bracket, aligning the outlet with the hose barb. Many Walbro pumps require using the black plastic insulator sleeve to prevent vibration. If your kit includes one, slide it onto the pump body before insertion.
  • Reinstall the grommet and top clip that hold the pump firmly. The pump should not wobble.
  • Wire the electrical connector. You may need to cut the stock connector and solder on the new ring terminals or use heat-shrink butt connectors. The Walbro pump uses two male spade terminals: polarity matters. Typically the red wire is positive (12V) and black is ground. Confirm with the pump datasheet. Use a multimeter to verify continuity if uncertain.

Important Fitment Notes

  • GD/GG (2002–2007): The Walbro 255 is a near-direct drop-in. You may need to trim the fuel hose that connects the pump outlet to the module top cap. Use a quality submersible fuel hose (not standard rubber) to prevent degradation.
  • GR (2008–2014): The module design is different. Some owners report needing to file down a plastic tab to clear the pump body. Check online forums like NASIOC or WRX Club for specific guidance for your month/year.
  • VA (2015–2021): The fuel pump is a different assembly requiring a “directional” pump. Walbro makes a specific direct-fit kit (F90000270). Verify before purchasing.

Reassembling the Fuel System

  1. Replace the tank seal gasket if it looks flattened or cracked. Apply a thin film of clean engine oil or silicone grease to the gasket to help it seat.
  2. Lower the pump module back into the tank. Align the orientation marker (usually a notch or arrow on the top cap) with the mark on the tank. Push down firmly.
  3. Install the retaining ring. Hand-tighten first, then use the tool to torque to 25–30 in-lb (do not overtighten—plastic rings crack). The notches should align with the orientation mark.
  4. Reconnect the fuel lines. Push each line onto the fitting until you hear a click. Pull back gently to confirm engagement.
  5. Reconnect the electrical harness. Ensure the locking tab snaps.
  6. Reinstall the access plate and the rear seat cushion.

Priming and Testing

Initial Prime

  1. Reconnect the battery negative terminal.
  2. Turn the ignition key to the ON position (engine off) for 2–3 seconds. You should hear a low hum from the fuel pump (the prime cycle). Turn the key OFF, wait 5 seconds, then repeat about 3–5 times. This purges air from the system.
  3. Inspect for leaks at every connection: the pump outlet hose, the fuel line quick-disconnects, and the tank seal. Use a flashlight and a rag to feel for moisture.

Engine Start and Final Check

  1. Start the engine. It may take a few extra cranks to fire on the first try because the lines are filling with fuel.
  2. Let the engine idle for 2–3 minutes. Monitor the fuel pressure gauge if you have one installed (target 43 psi at idle for most WRX models on returnless systems).
  3. Rev the engine to 3000 RPM and hold briefly. Listen for any hesitation or inconsistent idle that could indicate a faulty pump or loose wiring.
  4. Turn the engine off and recheck for leaks one more time. Fuel smell in the cabin is a common sign of a leaky quick-disconnect.

Data Logging (Optional)

If you have an AccessPort or other tuning tool, data log Fuel Pressure Actual and Fuel Pressure Target during a 3rd-gear pull from 2000–6000 RPM. The Walbro 255 should maintain target pressure within ±2 psi. If pressure drops, you may have a clogged filter, failing pump, or voltage drop (check pump wiring voltage at the connector under load).

Troubleshooting Common Issues

  • No prime sound: Check fuse #11 (or the fuel pump relay). Use a test light or multimeter at the pump connector. If you have 12V but no pump, polarity may be reversed or the pump is defective.
  • Fuel leaks from the pump outlet hose: The hose clamp may be loose or the hose not rated for submersion. Replace with EFI-rated submersible hose and use a proper constant-tension clamp.
  • Check Engine Light (P0087 or P0088): Fuel rail pressure too high/low. The Walbro 255 can overpower the factory pressure regulator if the pump is mounted incorrectly or the bypass orifice is blocked. On some WRX models, a fuel pressure regulator spacer or aftermarket FPR is required.
  • Loud whining noise from the rear seat: Normal for a Walbro pump—it is a gear-type pump and mechanically louder than the stock turbine pump. If the noise is excessively loud, check that the pump is correctly insulated by the rubber grommet.

Maintaining Your Upgraded Fuel System

  • Replace the fuel filter at every oil change for the first two changes after the pump install (more sediment can be dislodged).
  • Run at least 1/4 tank of fuel to keep the pump submerged and cool. Walbro pumps rely on fuel for lubrication and cooling.
  • Avoid repeated low-fuel runs—running the tank dry can suck air into the pump and cause cavitation.
  • Periodically check the wiring connectors for corrosion, especially if you live in a humid or salt-spray environment.

External Resources

Final Thoughts

The Walbro 255 fuel pump is one of the most rewarding upgrades for a modified WRX. It provides the headroom needed for larger injectors, ethanol blends, and aggressive turbo setups. By following this detailed guide—taking care with fuel line connections, correctly orienting the pump, and verifying prime and pressure—you can complete the install in a couple of hours with standard hand tools. Always prioritize safety, double-check your wiring, and don’t hesitate to consult model-specific forums if you hit an unexpected obstacle. With the fuel system sorted, your WRX will be ready for the next power step.