Installing A Fuel Pressure Regulator In A 3000Gt: Step-By-Step Guide

If you're experiencing issues with your Mitsubishi 3000GT's fuel pressure regulator, you may need to replace or adjust it. The fuel pressure regulator is responsible for maintaining fuel pressure and decreasing fuel pressure while the car is idling. Symptoms of a faulty fuel pressure regulator include a rough idle, difficulty finding the correct idle, and a rich-running engine, which can lead to poor gas mileage. While there are temporary workarounds, such as disconnecting the vacuum line from the throttle body to the FPR, it is not recommended to drive your car this way for an extended period. Instead, consider seeking professional assistance or attempting a DIY fuel pressure regulator setup, which typically costs around $250 for the necessary parts.

Disconnecting the vacuum line from the throttle body to the fuel pressure regulator

Before beginning any work on your vehicle, it is important to ensure you have the necessary tools and safety equipment. For this task, you will need basic hand tools such as wrenches and screwdrivers, as well as eye protection and gloves for safety. It is also recommended to have a repair manual specific to your vehicle make and model on hand for reference.

Locate the Fuel Pressure Regulator: The fuel pressure regulator is part of the engine's fuel system and is responsible for maintaining the correct fuel pressure. It is usually located near the throttle body, which controls the amount of air entering the engine.

Access the Vacuum Line: The vacuum line is a hose that connects the throttle body to the fuel pressure regulator. It may be secured with clamps or other fasteners. To disconnect it, you will need to locate the point where it attaches to the throttle body. This may require removing other components for better access, such as the intake manifold or air filter housing.

Disconnect the Vacuum Line: Once you have located the vacuum line, you can disconnect it from the throttle body. Be sure to cap or plug the open ports to prevent debris or contaminants from entering the fuel system. Label the vacuum line to ensure proper reconnection during reassembly.

Inspect the Vacuum Line: With the vacuum line disconnected, take this opportunity to inspect it for any signs of damage, cracks, or leaks. A damaged vacuum line can affect engine performance and fuel efficiency, so it is important to replace it if necessary.

Clean the Connections: Before reconnecting the vacuum line or installing a new fuel pressure regulator, clean the connections and ports to remove any dirt, grease, or debris. This will help ensure a proper seal and prevent leaks.

At this point, you can proceed with installing a new fuel pressure regulator or reconnecting the vacuum line to the original regulator. Be sure to follow the manufacturer's instructions and torque specifications for a secure and proper installation.

Remember, working on your vehicle's fuel system can be complex and requires careful attention to detail. If you are uncomfortable with any aspect of the procedure, it is always best to consult a qualified mechanic.

Capping the throttle body nipple and plugging the fuel pressure regulator line

The fuel pressure regulator (FPR) is responsible for maintaining fuel pressure and decreasing it while the car is idling. When you disconnect the vacuum line and cap the throttle body nipple, you increase the fuel pressure at idle, which can cause issues with fuel trims and lead to running lean under open loop.

While capping the throttle body nipple and plugging the FPR line may provide a short-term improvement in idle and low RPM performance, it is not recommended as a long-term solution. It can cause issues with fuel trims, leading to running lean and affecting the engine's performance. Additionally, the ECU will compensate for the increased fuel pressure, which can result in storing incorrect data and affecting the car's performance.

To properly address the issue, it is recommended to check for vacuum leaks, reset the idle, and replace the FPR with a new one. This will ensure that the fuel pressure is regulated correctly and the engine is receiving the appropriate amount of fuel, improving the car's performance and fuel efficiency.

It is important to note that the throttle body nipple and the fuel pressure regulator line are crucial components of the fuel system and any modifications or repairs should be done carefully to avoid potential issues with the engine's performance and fuel efficiency.

Bypass the fuel pressure regulator

To bypass the fuel pressure regulator (FPR) on a Mitsubishi 3000GT, you can try the following methods:

Method 1: Disconnecting the Vacuum Line

• Disconnect the vacuum line from the throttle body to the FPR.
• Cap the throttle body nipple and plug the FPR line.
• Start the car. Note that this method may only be a temporary solution and can affect fuel pressure and ECU settings.

Method 2: Upgrading the FPR

• Grab a vacuum source from the plenum and use a dedicated line.
• Connect the FPR to a Vac/Boost reference, such as any port on the back of the plenum.

Method 3: Patching the Solenoid

• Remove the solenoid.
• Patch the two hose ends that were on the solenoid back together or replace them with a new hose.

Method 4: Using a T-Connector

• Unhook the blue-dotted vacuum line going to the FPR and the red-dotted vacuum line going to the P port on the throttle body.
• Connect the open nipples with your own vacuum line using a T-connector.

Please note that bypassing the FPR is generally not recommended as a long-term solution. It can affect fuel pressure, engine performance, and fuel efficiency. It is suggested to use these methods temporarily and install a new FPR as soon as possible.

Checking for vacuum leaks

Before beginning the installation of a new fuel pressure regulator, it is important to diagnose the cause of the issue. In the case of a fuel pressure regulator problem, one of the possible causes is a vacuum leak. To check for vacuum leaks, follow these steps:

• Inspect the vacuum lines: Begin by carefully examining all the vacuum lines connected to the fuel pressure regulator and other engine components. Look for any signs of damage, cracks, or loose connections.
• Use a smoke machine: A smoke machine is a specialized tool that can be connected to the intake manifold of the engine. It generates smoke, which will escape from any leaks in the vacuum system, making them easier to identify. This is an effective method to locate hard-to-find leaks.
• Listen for unusual sounds: Start the engine and listen carefully for any unusual sounds, such as hissing or squealing noises. These sounds could indicate air escaping from a leak in the vacuum system.
• Use a vacuum gauge: Connect a vacuum gauge to the intake manifold. If the vacuum reading is lower than normal or fluctuates erratically, it may indicate a leak in the system.
• Check common leak areas: Some areas are more prone to leaks than others. Pay close attention to the connection between the intake pipe and the throttle body, as well as the vacuum lines themselves, as these are common leak points.
• Inspect the fuel pressure regulator: Since the fuel pressure regulator is a focus of your issue, carefully inspect it for any signs of damage, leaks, or malfunctions. This may include visual inspection as well as testing with appropriate tools.
• Re-secure connections: If you find any loose connections or fittings, tighten them and ensure they are secure. This may resolve the issue if the leak was caused by a loose connection.
• Replace damaged components: If you identify any damaged or cracked vacuum lines, replace them with new ones. This will ensure a proper seal and prevent further leaks.
• Repeat the testing: After making any necessary repairs or replacements, repeat the testing procedures to ensure that the vacuum leaks have been addressed. This may involve re-testing with the smoke machine, vacuum gauge, and listening for unusual sounds.
• Refer to factory service manual: If you are unsure about the specific vacuum lines or components in your Mitsubishi 3000GT, refer to the factory service manual for detailed diagrams and troubleshooting information.

Remember, checking for vacuum leaks is just one aspect of diagnosing fuel pressure regulator issues. There could be other factors at play, such as a faulty fuel pressure regulator, issues with the fuel injectors, or problems with the fuel filter. A comprehensive diagnosis, including testing fuel pressure and inspecting other engine components, may be necessary to pinpoint the exact cause of the problem.

Resetting the idle

First, check for any vacuum leaks, as these can cause serious idle issues. N/A's usually have leaks where the intake pipe connects to the throttle body and from old vacuum lines. Seal up any leaks you find to ensure the engine is properly sealed.

Next, make sure your TPS (Throttle Position Sensor) idle switch is closed at idle. Confirm that it is switching properly before moving on to the next step.

Reconnect the vacuum line to your FPR (Fuel Pressure Regulator). The FPR needs to be functioning properly to maintain the correct fuel pressure, especially at idle.

Allow your car to warm up fully. During this time, you can work on grounding the necessary pins to put the ECU into idle set mode.

Locate the OBDI port inside the car, usually down by the clutch pedal attached to the side of the small fuse box. Pin 10 needs to be grounded by attaching a wire to some bare metal.

Next, locate the small brown plug behind the passenger strut tower, behind the battery. Take the cap off and use a piece of wire to ground that plug as well.

With both pins grounded, try to start the car. It may not be happy about it, so if it won't stay running, turn the BISS (Base Idle Stop Screw) screw out a couple of turns and try again. If the BISS is all the way out and it still won't stay running, you may have a more serious problem that needs to be addressed before you can set the idle.

Once the car is idling, use a screwdriver to adjust the BISS screw to achieve your desired idle RPM. Turn the screw clockwise to lower the idle RPM and counter-clockwise to increase it. The target idle RPM for the 3000GT is around 700 RPM.

Remove the grounding wires and let the car idle for about 20 minutes to allow the ECU to adjust. The ECU stores the low trim adjustment/IAC step position every 4 minutes, so 20 minutes gives it a good baseline.

After the 20 minutes, your mid fuel trim/IAC step position should be stored, and your idle should be running smoothly. If it's still not running as it should, you may have more serious problems that require further diagnosis.

Performing these steps should help you reset the idle on your Mitsubishi 3000GT and improve its overall performance, especially at low RPMs.

Frequently asked questions