Relocating Vacuum Fuel Pressure: The Wrx Guide

The COBB Tuning Fuel Pressure Regulator Manifold Reference Relocation Kit is a popular choice for those looking to relocate their vacuum fuel pressure in the WRX. The kit includes everything you need to move the fuel pressure regulator's manifold pressure reference away from the #4 cylinder runner and into a plenum-based source, which can help prevent unwanted manifold pulsations. This relocation is similar to the method used in the previous generation 2004-2007 STI.

Fuel pressure regulator installation

Installing a fuel pressure regulator (FPR) can be a simple process, but it's important to take the necessary precautions and follow the correct steps to ensure a safe and effective installation. Here's a detailed guide on how to install a fuel pressure regulator, specifically focusing on the relocation of the vacuum fuel pressure on a WRX vehicle.

Preparation

Before beginning the installation, it's important to do your research and choose the right fuel pressure regulator for your vehicle. Consider the type of fuel delivery system and fuel pump you are using. It's also recommended to refer to your vehicle's repair manual for specific instructions. Additionally, ensure you have the necessary tools and safety equipment, such as rags or paper towels to catch any fuel spillage.

Relieving Fuel Pressure

Start by relieving the fuel pressure in your system. This can be done by removing the schrader valve cap and catching any fuel that squirts out with rags or paper towels. You can also depressurize the lines by removing the fuel pump fuse and cranking the car until it stalls and turns off.

Removing the Old FPR

Next, remove the vacuum hose from the top of the FPR. Then, use a wrench to remove the steel fuel line nut located below the FPR. The size of the wrench may vary, so refer to your vehicle's manual or a mechanic for the correct size. With a socket wrench, remove the bolts holding the FPR to the rail, and gently pull it off. Be careful when removing the bolts, as stripping them can lead to additional work.

Replacing O-Rings

Now, you can remove the old FPR's O-rings and replace them with new ones. Take the old O-rings to an auto parts store to ensure you get the correct replacements. It is generally a good idea to replace O-rings in fuel systems when performing maintenance.

Installing the New FPR

Before installing the new FPR, refer to its manual to identify the fuel IN/OUT ports. You may need to add thread sealant to the fittings and let it cure overnight, as per the sealant instructions. Reverse the removal process, ensuring that the new O-rings are properly seated and any fittings are tightened securely.

Final Steps

Connect the vacuum hose from the manifold to the FPR. Start the car and check for any leaks. If there are no leaks, adjust the fuel pressure to the recommended baseline for your vehicle. This can be done by loosening the lock nut and turning the hex key to raise or lower the pressure.

Additional Considerations

If you are relocating the vacuum source for the FPR, you may need to purchase a relocation kit, such as the COBB Tuning FPR Manifold Reference Relocation Kit for WRX vehicles. This kit allows you to move the FPR's manifold pressure reference away from an individual cylinder runner to a plenum-based source, reducing the impact of unwanted manifold pulsations.

Remember to always exercise caution when working with fuel systems, and if you are unsure about any part of the process, consult a professional mechanic.

Cobb Tuning FPR Manifold Reference Relocation Kit

The COBB Tuning FPR Manifold Reference Relocation Kit is designed to improve the performance and stability of your vehicle's fuel pressure regulator. This kit is an ideal solution for those seeking to relocate the FPR reference line to a more stable pressure source, enhancing the efficiency of the fuel system.

One of the key benefits of this kit is its ability to move the fuel pressure regulator's manifold pressure reference away from the #4 cylinder runner. By relocating it to a plenum-based source, similar to the setup used in the 2004-2007 STI models, you can prevent unwanted manifold pulsations from impacting the FPR. This is because the plenum is a common area of the manifold that takes into account the average vacuum and boost of all cylinders, rather than just a single cylinder.

The COBB Tuning FPR Manifold Reference Relocation Kit is a comprehensive solution, including all the necessary components for a successful relocation. It comes with a 4mm and 6mm silicone vacuum line, a reducing "T" fitting, and even black zip ties to secure the setup. This kit is compatible with a range of Subaru models, specifically the WRX STI produced between 2008 and 2021.

By utilising this kit, you can achieve a more stable and reliable fuel pressure reference, resulting in improved engine performance and a smoother driving experience. It's important to note that this part is not emissions-related, so it can be used on Emission Controlled Vehicles without any concerns. With its easy installation and complete set of parts, the COBB Tuning FPR Manifold Reference Relocation Kit is a great choice for anyone looking to optimise their vehicle's fuel system.

Fuel system maintenance

Overview

The fuel system's job is to maintain a proper fuel demand that will eventually be sprayed from the fuel injectors into the intake stream and the combustion chamber. The fuel system consists of the fuel tank, fuel pump, sending fuel lines, fuel rail, fuel injectors, fuel pressure regulator, and, in the case of a return fuel system, fuel return lines.

Testing Fuel Pressure

To test fuel pressure, you will need a special gauge as the pressure can exceed 10kpsi. The WRX ECU monitors both fuel pressures as it is a returnless system. A scan tool can verify pressures, and the ECU should trigger a CEL if something is wrong.

Relocating the Fuel Pressure Regulator

The COBB Tuning Fuel Pressure Regulator Manifold Reference Relocation Kit includes everything needed to relocate the FPR reference line to a more stable pressure source. This helps prevent unwanted manifold pulsations from affecting the FPR.

Fuel Injectors

You should only change your fuel injectors when they are starting to exceed a certain duty cycle. The industry standard is a maximum of 80-85% duty cycle. Anything higher, and you run the risk of overheating, which will cause them to not open/close efficiently or result in plain failure.

Fuel Pump

The fuel pump is rated typically by lbs per hour or gallons per hour. The equation to calculate the flow rate is: Flow Rate = Horsepower x BSFC Flow Rate = X lbs/hr.

Troubleshooting

If your engine is cutting power completely with very little increase in rpms or speed, it could be due to a dirty fuel filter causing the pump to experience a reduction in flow intermittently.

Fuel injectors

The fuel injectors in a WRX are responsible for delivering the precise amount of fuel to the engine, ensuring optimal performance and fuel efficiency. They are an essential component of the fuel system, and there are several options available for WRX owners.

Upgraded fuel injectors can be purchased from several manufacturers, including COBB Tuning, Fuel Injector Clinic, Grams Performance, and IAG Performance. These injectors are designed to deliver a more precise amount of fuel to the engine, resulting in increased horsepower and improved engine performance.

When considering fuel injector upgrades, it is important to match the injector to the specific WRX model and year. For example, the Fuel Injector Clinic offers injector sets specifically designed for the 2002-2014 WRX and the 2007+ WRX and STi models. These injectors come in various sizes, such as the 2150cc, 1650cc, 1440cc, 1200cc, 1000cc, 775cc, and 650cc options, each tailored to the unique fuel delivery requirements of the WRX engine.

Additionally, the COBB Tuning Fuel Pressure Regulator Manifold Reference Relocation Kit is a popular choice for WRX owners looking to optimise their fuel system. This kit allows for relocating the fuel pressure regulator's manifold pressure reference away from the #4 cylinder runner and into a plenum-based source. By doing so, it helps prevent unwanted manifold pulsations from affecting the fuel pressure regulator, resulting in a more stable pressure source. This relocation kit is suitable for the 2008-2020 WRX STi and includes all the necessary components for a straightforward installation.

Fuel pump

The fuel pump is a vital component of your car's fuel system, ensuring that fuel is delivered from the tank to the engine. When upgrading your fuel system, it's important to choose a fuel pump that can keep up with the demands of your engine and other performance modifications.

There are a variety of fuel pump options available for the WRX, each with its own unique specifications and features. For example, the Walbro 255LPH fuel pump is a popular choice for the Subaru platform, but more powerful options are also available, such as the AEM 340LPH E85 Hi-Flow fuel pump. This pump is designed to withstand the low lubricity characteristics of ethanol and methanol fuels and is compatible with ethanol fuels up to E100, methanol fuels up to M100, and all types of gasoline. Its compact, short body design makes it ideal for fuel tanks with tight tolerances.

When choosing a fuel pump, it's important to consider the specific requirements of your vehicle and your performance goals. For instance, if you're planning to increase the horsepower of your WRX, you'll need a fuel pump that can keep up with the increased fuel demands. Additionally, it's worth noting that some fuel pumps may require additional modifications, such as a new fuel pressure regulator or a remap, to ensure optimal performance and prevent issues like overfuelling.

Another option for modifying your fuel system is to relocate the fuel pressure regulator's manifold pressure reference. The COBB Tuning Fuel Pressure Regulator Manifold Reference Relocation Kit allows you to move the reference line to a more stable pressure source, such as the plenum. This helps prevent unwanted manifold pulsations from affecting the fuel pressure regulator, resulting in more stable fuel pressure and improved performance.

By carefully selecting and modifying your fuel pump and related components, you can ensure that your WRX's fuel system can support your desired performance enhancements while maintaining reliability and efficiency.

Frequently asked questions