Adjusting Fuel Pressure Regulator In Wrx: A Step-By-Step Guide

If you're looking to adjust the fuel pressure regulator on your WRX, you've come to the right place. This guide will take you through the process step-by-step, offering helpful tips and tricks along the way. But before we dive into the specifics, let's cover some basics. All cars with a return-type fuel system require a fuel pressure regulator, and in most cases, you'll find the OEM regulator at the back of the right bank's fuel rail. Now, let's get started on the adjustment process.

Installing a new FPR

Firstly, ensure you have the necessary parts: a fuel hose with a 5/16" diameter, fuel hose clamps, brass hose menders (5/16" or as needed), a '06 STI Fuel Supply Damper, and a '06 STI Fuel Return Damper. It is also recommended to have safety goggles and gloves for your protection.

Now, follow these steps:

• Remove the OEM damper and FPR assembly. This will involve disconnecting the fuel lines and vacuum lines carefully.
• Connect the '06 supply side damper to the original fuel supply hose.
• Connect the other side of the damper to the inlet of the fuel rail.
• Connect the fuel rail outlet to the inlet of the new FPR.
• Connect the FPR outlet to the '06 return damper.
• Connect the return damper to the return hose.
• Connect the FPR vacuum hose to the intake manifold where the OEM FPR was connected.
• Set the FPR to the recommended fuel pressure, typically 43.5 psi for WRXs, with the vacuum hose detached and blocked/kinked.
• Reattach the vacuum hose to the FPR.

It is important to ensure all connections are secure and that there are no leaks. Use zip ties to secure the vacuum line to prevent it from popping off. Additionally, you may need to adjust engine load compensation tables and other settings depending on your specific setup.

Always refer to a professional mechanic or a detailed guide specific to your vehicle for the most accurate and safe instructions.

Setting the correct pressure

To set the correct pressure, follow these steps:

• Ensure the vehicle is turned to the “ON” position to activate the fuel pump, but do not start the engine.
• Detach the vacuum hose line from the fuel pressure regulator (FPR). It's important to block or kink this line while adjusting the pressure to prevent any issues.
• Using an adjustment screw or similar tool, adjust the fuel pressure regulator to the desired setting. In this case, you should set it to 43.5 psi.
• Once the desired pressure is achieved, reattach the vacuum hose line to the FPR. Ensure it is securely connected.

It's worth noting that you may need to adjust the engine load compensation tables of your tune after setting the correct fuel pressure. Additionally, if you have made significant modifications to your fuel system or are running a larger fuel pump, it is recommended to consult a professional tuner to fine-tune the fuel delivery and ensure optimal performance.

Remember, adjusting the fuel pressure can impact the performance and safety of your vehicle. Always exercise caution and refer to a professional if you're unsure about the process.

Replacing the stock FPR

When installing a new FPR, you will need the following additional parts: a 5/16" diameter fuel hose, fuel hose clamps, brass hose menders 5/16" (this may vary depending on how you connect the hoses), a '06 STI fuel supply damper, and a '06 STI fuel return damper. First, remove the OEM damper and FPR assembly. Then, connect the '06 supply side damper to the original fuel supply hose and connect the other side of the damper to the inlet of the fuel rail. Next, connect the fuel rail outlet to the new FPR inlet (side) and the FPR outlet (bottom) to the '06 return damper. Connect the return damper to the return hose and the FPR vacuum hose to the IM where the OEM FPR used to be.

Finally, set the FPR to 43.5 psi, which is the OEM pressure. You may deviate from this to suit your fuel requirement. It is important to note that you should set the pressure with the vacuum hose unattached and blocked or kinked. Once the pressure is set, reattach the vacuum hose to the FPR.

Adjusting the FPR for WRX

Adjusting the fuel pressure regulator (FPR) on your WRX is a relatively straightforward process, but it requires careful attention to detail and a few specific tools. Here is a step-by-step guide to help you through the process.

Step 1: Prepare Your Car

Before beginning the adjustment, it is important to ensure your safety and the safety of your vehicle. Put on a pair of safety goggles to protect your eyes from any fuel spray. Then, depressurise the fuel lines by pulling the E/G fuse from the fuse box and cranking the engine a few times.

Step 2: Locate and Remove the FPR

The FPR on a WRX is located next to the air intake box on the passenger side of the car. To remove it, you will need to:

• Loosen two 10mm bolts
• Loosen the clamp on the fuel line and slowly wiggle the FPR out, being careful not to damage the vacuum line connected to the intake manifold
• Secure the vacuum line with zip ties to prevent it from popping off, a common problem with this procedure

Step 3: Install the New FPR

When installing a new FPR, such as the Tomei Type L or Type S, you will need to acquire additional parts, including fuel hoses, fuel hose clamps, brass hose menders, and dampers. The specific parts required may vary depending on your car model and the FPR you are installing. Be sure to consult a mechanic or a forum for specific instructions for your vehicle.

Once you have the necessary parts, follow these general steps:

• Remove the OEM damper and FPR assembly
• Connect the supply side damper to the original fuel supply hose, and then connect the other side of the damper to the inlet of the fuel rail
• Connect the fuel rail outlet to the FPR inlet, and then connect the FPR outlet to the return damper
• Connect the return damper to the return hose
• Connect the FPR vacuum hose to the intake manifold where the OEM FPR was previously connected

Step 4: Adjust the FPR

Now it's time to adjust your new FPR. First, turn your car to the "ON" position to activate the fuel pump, but do not start the car. Adjust the FPR to 43.5 psi, which is the OEM pressure for idle. You may deviate from this pressure to suit your fuel requirements, but be sure to consult a professional or a tuning specialist before doing so.

Finally, reattach the vacuum hose to the FPR.

Additional Considerations

• It is important to replace the O-ring if necessary. You can also apply a small dab of lube or dish soap to the O-ring before installation.
• Be careful not to over-tighten the bolts during installation, as this can damage the O-ring and cause leaks.
• Ensure that the fuel lines are connected correctly. Connecting them incorrectly can result in poor idle and running issues.
• If you are planning to use E85 fuel, you may need to upgrade your fuel pump and injectors, and you will need to consult a tuner about the appropriate maps for switching between E85 and non-E85 fuels.

FPR maintenance

Overview

The Fuel Pressure Regulator (FPR) in your WRX is responsible for maintaining the correct fuel pressure in the fuel injection system. It ensures that the fuel injectors receive the proper amount of fuel at the correct pressure, which is essential for the engine to run smoothly and efficiently.

When to Adjust or Replace the FPR

There are a few signs that may indicate it's time to adjust or replace your FPR. If you're experiencing issues such as rough idling, decreased fuel efficiency, difficulty starting the engine, or a "Check Engine" light illuminating, it could be due to a faulty or improperly adjusted FPR. Additionally, if you've recently installed performance modifications, such as a larger fuel pump or higher-flow fuel injectors, adjusting the FPR may be necessary to compensate for the increased fuel demand.

Adjusting the FPR

The process of adjusting the FPR can vary slightly depending on the specific model of your WRX and the type of FPR you have installed. However, here are some general steps to follow:

• Park your car on a level surface and engage the parking brake.
• Open the hood and locate the FPR. It is usually found near the fuel rail or fuel lines.
• Disconnect the vacuum hose from the FPR. This hose is responsible for providing manifold pressure information to the FPR.
• With the vacuum hose disconnected, start the engine and let it idle.
• Using the adjustment screw on the FPR, adjust the fuel pressure to the specified value. For most WRX models, the recommended fuel pressure at idle is around 43.5 psi. You may need a fuel pressure gauge to accurately measure this.
• Once the desired fuel pressure is achieved, carefully reconnect the vacuum hose to the FPR.
• Re-check the fuel pressure after reconnecting the vacuum hose to ensure it is still within the specified range.

Replacing the FPR

If your FPR is faulty or damaged, you may need to replace it entirely. Here are some general steps for replacing the FPR:

• Park your car on a level surface and engage the parking brake.
• Disconnect the negative terminal of the battery to prevent any accidental electrical shorts.
• Locate the FPR and identify the fuel lines and electrical connections attached to it.
• Relieve the fuel system pressure by removing the fuel pump fuse and cranking the engine a few times.
• Disconnect the fuel lines and electrical connections from the FPR. Be sure to use appropriate safety gear, such as safety goggles, when working with fuel lines.
• Remove the FPR by unscrewing or unbolting it from its mounting location.
• Install the new FPR by following the previous steps in reverse. Ensure all connections are secure and properly tightened.
• Reconnect the negative battery terminal.
• Start the engine and check for any fuel leaks or unusual noises.

Additional Considerations

• It is important to consult a professional mechanic or a trusted workshop manual for specific instructions pertaining to your vehicle's make, model, and year.
• Always exercise extreme caution when working with fuel system components. Ensure proper ventilation and avoid open flames or sparks.
• When adjusting or replacing the FPR, it is recommended to have a qualified tuner assess your vehicle's fuel system and engine management settings to ensure optimal performance and safety.

By following these maintenance procedures and guidelines, you can help ensure that your WRX's fuel system operates efficiently and reliably.

Frequently asked questions