Fuel Pressure Regulator: Fd Rx7 Installation Guide

The fuel pressure regulator in the Mazda RX-7 is an important component of the fuel system, ensuring that the engine receives the correct amount of fuel and maintaining the right fuel pressure. The stock fuel system on the 3rd generation RX-7 can support upwards of 380HP with an appropriate ECU upgrade. However, the first component that may need replacing is the stock fuel pump. Upgrading to a high-flow fuel pump, such as the Denso pump, can significantly improve fuel delivery. Additionally, it is recommended to regularly change the fuel filter, as a clogged filter can impede fuel flow and affect engine performance. The fuel pressure regulator itself should be set to a base pressure of around 38 psi, and changing this pressure will also alter the fuel mixture, requiring a re-tune of the car.

Fuel pressure regulator and fuel pump

The fuel pressure regulator and fuel pump are essential components of the fuel system in an FD RX7. The fuel pump supplies fuel to the engine, while the fuel pressure regulator controls the fuel pressure to ensure the engine receives the correct amount of fuel for proper combustion.

The stock fuel pump in the FD RX7 is known to be inadequate for supporting higher horsepower levels and is often one of the first components that need replacing. Upgrading to a high-flow fuel pump, such as the OE manufacturer Denso pump, can provide the necessary fuel flow for modified engines. This pump is a direct bolt-in replacement and does not require any additional modifications, making it a popular choice for FD RX7 owners.

The fuel pressure regulator plays a crucial role in maintaining the appropriate fuel pressure. The stock fuel pressure in the RX7 is typically around 38 PSI at 0 manifold pressure. When adjusting the fuel pressure, it is important to use a 1:1 boost-compensating regulator to ensure the fuel pressure increases with boost pressure. This helps the injectors deliver the correct amount of fuel, especially during boost.

There are two types of fuel pressure regulators: adjustable and rising-rate (RRFPR). Adjustable regulators allow you to set a specific fuel pressure, which is useful if you want to raise the fuel pressure above the stock level. RRFPRs, on the other hand, increase fuel pressure relative to the boost pressure. For example, a 2:1 RRFPR will increase the fuel pressure by 2 psi for every 1 psi of boost pressure.

When installing an aftermarket fuel pressure regulator, it is important to consider the location of the fuel pressure gauge sender. Placing it between the stock regulator and the aftermarket regulator will result in a zero reading until the engine is under boost. This is because the stock regulator will always try to reduce the line pressure, and the actual fuel pressure will be the sum of the pressure added by the aftermarket regulator and the boost pressure.

Additionally, it is crucial to maintain the fuel system by regularly changing the fuel filter and addressing any leaks. The Fuel Pulsation Damper (FPD) in the FD RX7 is known to fail after approximately 60,000 miles, leading to high-pressure fuel leaks and potential engine fires. Upgrading or bypassing the FPD can help prevent such issues.

RX7 fuel system

The fuel system of an RX7 is a complex and important component of the vehicle's overall performance and safety. Here is a detailed overview of the RX7 fuel system, specifically focusing on the fuel pressure regulator and related components:

Fuel Pressure Regulator

The fuel pressure regulator plays a crucial role in maintaining the appropriate fuel pressure in the RX7's engine. The regulator ensures that the fuel pump delivers fuel at the correct pressure to the engine, optimizing performance and fuel efficiency. The ideal fuel pressure for the RX7 engine is around 38 PSI at 0 manifold pressure. However, some owners choose to run their vehicles at slightly lower or higher pressures, depending on personal preferences and modifications.

Fuel Pump

The stock fuel pump in the RX7 is designed to handle fuel requirements at near-stock levels. Upgrades to the engine or performance enhancements may require an upgraded fuel pump to meet the increased fuel demands. Aftermarket options, such as the high-flow fuel pump by Denso, offer higher flow rates and improved reliability without the need for additional modifications.

Fuel Injectors

The fuel injectors play a critical role in delivering the precise amount of fuel required by the engine. The stock fuel system in the RX7 uses two 550cc injectors for primaries and two 850cc injectors for secondaries, which activate at higher RPMs. It is important not to push the injectors beyond 80%-85% duty cycle for reliability reasons. Upgrading the fuel injectors can be a viable option for those seeking more power and precise tuning.

Fuel Pulsation Damper (FPD)

The FPD is a crucial component in the RX7's fuel system, designed to reduce high-pressure fuel pulses from the fuel pump. However, the FPD is known to fail after approximately 60,000 miles, leading to fuel leaks from the fuel rails under the Upper Intake Manifold (UIM). This failure can result in engine fires and significant damage. Therefore, regular maintenance and replacement of the FPD are essential to prevent such issues.

Fuel Filter

Maintaining a clean fuel system is vital for the RX7's performance and longevity. The fuel filter should be replaced regularly, ideally every 30,000 miles or 24 months. Failing to do so can lead to debris clogging the injectors and fuel lines, resulting in impaired fuel flow and potential engine damage.

Fuel Pressure

The fuel pressure in the RX7's fuel system is critical for optimal performance. Adjusting the fuel pressure can be done by tuning the engine or modifying the fuel pressure regulator. However, changing the fuel pressure will also alter the air-fuel mixture, requiring a re-tune of the engine for proper performance and fuel efficiency.

In conclusion, the RX7 fuel system is a complex and critical component of the vehicle's overall performance and reliability. Proper maintenance, including regular replacement of the fuel filter and FPD, is essential to prevent issues such as fuel leaks and engine fires. Upgrades to the fuel pump and fuel injectors can also be considered for enhanced performance, especially if the vehicle has been modified beyond stock specifications.

Fuel pulsation damper

A fuel pulsation damper (FPD) is a device used to regulate the oscillation of fuel caused by the injectors opening and closing. It uses a diaphragm to absorb pulses or waves in the fuel, smoothing out fuel delivery.

The need for a fuel pulsation damper is a topic of debate. Some say it is not necessary, while others argue that it is essential to prevent engine fires caused by the pulsation damper failing. The failure of the FPD causes high-pressure fuel to leak from the fuel rails under the Upper Intake Manifold (UIM). This can lead to engine fires and failures, as well as damage to the front rotor, rotor housing, and upgraded turbo.

The Mazda RX7 is equipped with an FPD that is prone to failing and causing engine fires. It is recommended to replace the FPD before it fails to prevent potential fire risks. The FPD typically fails after 60,000 miles but has been known to fail sooner.

If you are using an aftermarket fuel pressure regulator, it may have dampening capabilities built-in, eliminating the need for an additional damper. Mounting the aftermarket regulator close to the fuel rail will also help to remove any need for additional dampening.

Fuel pressure and horsepower

Fuel pressure regulators are essential components of a car's fuel system, ensuring the engine receives the appropriate amount of fuel for optimal performance. The fuel pressure regulator controls the fuel pressure in the system, maintaining the correct fuel mixture for the engine. Making adjustments to the fuel pressure can impact the horsepower of the vehicle.

The Mazda RX-7, for example, has a fuel pressure of about 38 psi at 0 manifold pressure. Some owners choose to run their vehicles at slightly lower pressures, around 36 psi, using a 1:1 boost-compensating regulator. Adjusting the fuel pressure can affect the fuel mixture, and it is recommended to re-tune the car after making such changes to ensure the engine runs smoothly.

The relationship between fuel pressure and horsepower is intricate. Increasing the horsepower of a vehicle often requires modifications to the engine, such as adding a turbocharger or supercharger. These modifications can increase the airflow to the engine, necessitating a corresponding increase in fuel delivery to maintain the desired air-fuel ratio. As a result, higher-flow fuel injectors become necessary to meet the engine's increased fuel demands.

Additionally, the fuel pump plays a crucial role in ensuring sufficient fuel supply for the desired horsepower. The fuel pump's flow rate must be adequate to deliver the required amount of fuel to the engine. For example, a rule of thumb is that a fuel pump should be able to deliver 10 gallons per hour for every 100 horsepower to prevent a lean situation at high rpm.

It is important to note that adjustments to the fuel pressure and fuel delivery system should be made with caution. Overly high fuel pressure or an insufficient fuel supply can lead to adverse effects, such as an overly rich fuel mixture or, in extreme cases, engine damage. Therefore, it is always recommended to consult with a professional or a trusted forum for specific advice regarding your vehicle's fuel system and horsepower goals.

Fuel pump relay

The fuel pump relay is an important component of the Mazda RX-7's fuel system. It controls the fuel pump's operational voltage, ensuring that the pump receives the correct amount of power to function effectively.

If you're experiencing issues with your fuel pump, it's crucial to troubleshoot the problem to identify the root cause. In some cases, the issue may lie with the fuel pump relay. Here are some steps and considerations to help diagnose and address problems related to the fuel pump relay in your FD RX7:

• Symptoms and Diagnosis: One of the most common signs of a faulty fuel pump relay is a lack of fuel reaching the engine, resulting in difficulty starting the car or poor engine performance. If you suspect a problem with the fuel pump relay, start by checking the voltage at the relay. Use a multimeter to test the voltage; if it's significantly lower than the expected 12 volts, the relay may be faulty.
• Checking the Relay: The fuel pump relay in the FD RX7 is typically located in the relay box or the fuse box. Refer to your FD RX7's manual or consult a trusted online forum to pinpoint the exact location of the relay. Once located, inspect the relay for any signs of damage, corrosion, or loose connections.
• Testing and Replacement: If the relay appears damaged or you continue to experience fuel pump issues, consider testing the relay by bypassing it and hardwiring the fuel pump directly to the battery. If the fuel pump operates normally when hardwired, the issue is likely with the relay or the wiring. In such cases, replacing the fuel pump relay may be necessary. Ensure you purchase a compatible replacement relay, such as the 93-95 Rx7 Fuel Pump Relay (NF01-18-821), which fits the FD RX7.
• Upgrades and Modifications: If you're planning to upgrade your fuel pump or make other performance modifications, it's essential to ensure that the fuel pump relay can handle the increased voltage or current demands. Consult with a professional or experienced FD RX7 enthusiasts before making significant changes to your fuel system.
• Fuel Pressure Regulator: While troubleshooting fuel pump issues, it's worth checking the fuel pressure regulator for proper adjustment. The stock RX-7 typically has a fuel pressure of around 38 PSI at idle, and this pressure can be adjusted using the fuel pressure regulator. An incorrectly adjusted regulator can lead to fuel starvation or over-fuelling issues.
• Other Considerations: In addition to the fuel pump relay, there are other components in the fuel system that can cause similar issues. These include the circuit opening relay, the fuel pump resistor, and the fuel pump itself. Ensure that you thoroughly diagnose the problem by checking these components and their associated wiring.

Remember always to refer to your FD RX7's service manual or seek assistance from a qualified mechanic if you're uncomfortable performing these diagnostics and repairs. Working on fuel systems can be dangerous, so prioritize your safety and consult experts whenever needed.

Frequently asked questions