Replacing The Fuel Pressure Regulator In A 3000Gt Vr4

The fuel pressure regulator (FPR) in a Mitsubishi 3000GT VR-4 is responsible for maintaining constant pressure across the fuel injectors. Replacing the FPR can be necessary if you're experiencing drivability issues, poor gas mileage, or engine damage due to an incorrect amount of fuel being delivered to the engine. This process involves releasing the pressure from the fuel system, removing the old FPR, and installing a new one, ensuring a proper seal and correct fuel pressure.

Removing the factory fuel pressure regulator

The fuel pressure regulator (FPR) is an important component of your Mitsubishi 3000GT VR-4's fuel system, as it maintains a constant pressure across the fuel injectors. The factory FPR is not adjustable and has a limit on the maximum fuel flow. Upgrading to an aftermarket FPR may become necessary if you've installed a high-flow fuel pump or want to accommodate dual feed and return lines.

Here's a step-by-step guide to removing the factory FPR:

• Relieve fuel line pressure: Access the fuel pump by removing the rear storage compartment carpet, particle board floor, spare tire, and passenger-side storage bin. Disconnect the electrical connector and try to start the engine – it shouldn't start as the fuel pump has no current.
• Move items out of the way: To access the FPR and the rear fuel rail, move and tie components like the PCV hose, CAS connector, and triple clamp on the plenum out of the way. You may also need to remove the air filter and MAS.
• Remove the battery and washer tank: Follow the instructions for your specific model to remove the battery, tray, and washer tank to gain better access to the bottom end of the fuel return hose.
• Remove the fuel return hose: Place a rag under the hose to catch any gasoline. Use pliers to loosen and slide off the clamp, then gently twist and pull the hose off the metal pipe. Repeat this process to remove the return hose from the FPR.
• Remove the factory FPR: Start by removing the vacuum hose on top of the FPR. Then, remove the two 10-mm hex cap screws that attach the FPR. Pull the FPR out slowly and firmly.
• Remove the factory solenoids: The firewall area is where you'll mount the new FPR, so you'll need to remove the fuel pressure control solenoid and move the purge canister and EGR control solenoids to the left. Disconnect the hoses and wiring harness from the solenoid. Press "back" and "down" on the solenoid lip to slide it off its bracket.

Once you've completed these steps, you'll have successfully removed the factory FPR and will be ready to install your aftermarket FPR.

Installing the new fuel pressure regulator

The first step in installing the new fuel pressure regulator (FPR) is to make and paint a new bracket for it. Cut and drill a piece of 1/16"-thick aluminium sheet, rounding the corners with a file. Paint the bracket using premium Rust-Oleum Flat Black Spray Enamel and allow several days for the paint to dry.

Next, relieve the fuel line pressure and remove the factory FPR. Remove the spare tire and the passenger-side storage bin in the rear storage compartment. Disconnect the electrical connector at the fuel pump and try to start the engine – it shouldn't start because the fuel pump has no current. Remove the negative cable from the battery.

Now, move items out of the way near the factory FPR, including the PCV hose, CAS connector, and triple clamp on the plenum. Remove the battery and washer tank, then place a rag under the fuel return hose to catch any gasoline. Loosen the clamp and slide it off the hose, then gently twist and pull the hose off the metal pipe. Similarly, remove the return hose from the factory FPR.

Remove the two 10-mm hex cap screws that attach the factory FPR and slowly pull it away from the engine. Measure the opening of the FPR into the rail – this will be important for fitting the new FPR.

At this point, you can install the fuel rail adapter. Apply engine oil to the o-ring for the EK2MFG fuel rail adapter and roll the o-ring onto the non-threaded end of the adapter, then press it firmly into the fuel rail. Put the split spring washers on the socket head cap screws and tighten them using a 5-mm hex key.

Now, it's time to build the FPR assembly. Add a -6 AN port plug to the right side of the A1000-6, along with an o-ring. Thread a -6 AN flare union into the left port, adding an o-ring to create a seal. Connect the factory return hose to the lower port of the A1000-6 using a -6 AN to -4 AN union reducer. Tighten all connections by hand for now, as you'll need to test the alignment and measure the return hoses for length.

Attach the assembled FPR to the painted bracket, then attach the bracket to the solenoids bracket using the upper two bolts. You may need to manoeuvre the cruise control actuator cable to get the lower return hose fittings in place. Position the lower fittings and tighten them by hand, then attach the pressure sensor fittings if you're using a fuel pressure sensor.

Now, make the upper return hose from the rail to the FPR. Cut the Earl's Perform-O-Flex hose to length, then attach Earl's anodized Auto-Fit hose ends. Secure the hose ends to the hose with duct tape, then use a vice and a 3/4" open-end wrench to tighten the socket onto the nipple.

For the lower return hose, cut the factory return hose to length and trim back the protective outer plastic sheath. Connect the hose to the FPR and the metal factory return tube using screw-type hose clamps.

Finally, attach the hoses. Reconnect the harness connector at the fuel pump and use the fuel pump check terminal to supply voltage to the fuel pump, pressurising the lines. Connect the battery and touch jumper wires to the correct terminals. You should hear the fuel pump running. Inspect your work for leaks and repair any issues.

Once you're happy with the installation, put everything back in place. Reconnect any hoses or harness connectors and brackets that you removed, and reinstall the battery tray, washer tank, MAS, air filter, and battery.

The final step is to set the fuel line pressure. Connect a fuel pressure sensor or gauge to the FPR and loosen the lock nut at the base of the adjustment screw. Turn the screw clockwise to increase fuel line pressure. Start the engine and adjust the pressure to the recommended level, then reconnect the vacuum reference hose. The fuel pressure should reduce by about 7-10 psi. Tighten the lock nut with a 9/16" wrench to secure the setting.

Making the upper return hose from the rail to the FPR

Next, you will need to remove the factory FPR and return hose. This will involve relieving the fuel line pressure and moving some components out of the way to access the FPR and return hose. Place a rag under the hose to catch any gasoline that may spill and always wear safety glasses to protect your eyes. Use pliers to loosen the clamp and slide it off the hose, then gently twist and pull the hose off the metal pipe.

Now, you can install the new fuel rail adapter. Apply a small amount of engine oil to the o-ring and roll it onto the non-threaded end of the adapter. Firmly press the adapter into the fuel rail, ensuring that the mounting holes line up. Tighten the screws using a hex key.

To connect the upper return hose to the FPR, you will need to use Earl's Performance Plumbing Perform-O-Flex hose and the appropriate AN fittings. Cut the hose to the appropriate length and attach the hose ends that match your AN fittings. Earl's recommends using their Swivel-Seal, Auto-Fit, or Auto-Mate hose ends for a secure connection. Follow the instructions provided by Earl's for attaching the hose ends correctly.

Finally, attach the hoses to the FPR and fuel rail adapter, tightening the fittings by hand first and then using a wrench for a secure connection. Be careful not to over-tighten the aluminum AN fittings, as 10-12 ft-lbs of torque is sufficient. With the hoses connected, you can now pressure test your work and reconnect any components that were moved out of the way.

Making the lower return hose from the FPR

To make the lower return hose from the FPR, you will need to reuse the factory return hose. First, cut the hose to fit and trim back the protective outer plastic sheath by about 2 inches. Then, route the hose over towards the FPR and slide the spring clamp onto it. Connect the hose to the FPR and tighten the clamp. Finally, route the other end of the hose onto the metal return tube near the fuel filter and secure it with another clamp.

Attaching the hoses

Prepare the Hoses:

Before you begin, ensure you have the correct hoses and fittings for your specific fuel pressure regulator. You will need two hoses: an upper hose that connects the fuel rail to the FPR, and a lower hose that connects the FPR to the metal return tube near the fuel filter.

For the upper hose, Earl's Performance Plumbing Perform-O-Flex hose is an excellent option. This hose is braid-protected and designed to withstand fuel and high temperatures. You will also need two 90-degree -4 AN hose ends to connect the hose to the fuel rail and FPR.

For the lower hose, you can reuse the factory return hose, but it will need to be cut to the appropriate length. Alternatively, you can purchase a new hose with an inside diameter of about 7/32" and use screw-type hose clamps for a secure connection.

Attaching the Upper Hose:

• Start by attaching the 90-degree -4 AN hose end to the upper port of the FPR. Hand-tighten the fitting, and then use a wrench to tighten it further. Be careful not to over-tighten, as too much torque can damage the aluminum fittings.
• Next, attach the other end of the upper hose to the fuel rail. Again, hand-tighten the fitting first, and then use a wrench to secure it in place. Ensure that the hose is routed through the engine bay without any kinks or obstructions.

Attaching the Lower Hose:

• For the lower hose, you will need to attach it to the metal return tube near the fuel filter. This can be a tight fit, so you may need to manoeuvre the hose carefully around other components, such as the cruise control actuator cables.
• Slide the factory spring hose clamp onto the lower hose, and then attach the hose to the FPR. Ensure that the hose is securely clamped to prevent leaks.
• Now, route the lower hose towards the FPR and connect it to the corresponding port. Again, hand-tighten the fitting first, and then use a wrench to secure it in place.

Final Steps:

Once both hoses are attached, it is important to pressure test your work to check for leaks. Reconnect the electrical connector at the fuel pump and use a small jumper wire to supply voltage to the fuel pump, pressurising the lines. Inspect your work for any signs of leaks and ensure that all connections are secure.

If you have a fuel pressure sensor or gauge, you can now adjust the fuel line pressure to the recommended levels. For turbo DOHC models, the pressure should be between 295 and 315 kPa (42.7 to 45.6 psi). For SOHC and non-turbo DOHC models, the pressure should be between 330 and 350 kPa (47.8 to 50.7 psi).

Finally, reconnect any hoses or brackets that you may have moved during the installation process, and ensure that all components are securely fastened and routed correctly.

Frequently asked questions