Lowering Fuel Pressure In An Rx7 Fc: A Step-By-Step Guide

The fuel pressure in an RX7 FC can be decreased by adjusting the fuel pressure regulator. The stock fuel system on the 2nd generation Turbo II RX-7 can support upwards of 300 horsepower with an appropriate ECU upgrade. However, the first component that may need replacing is the stock fuel pump. Upgrading the fuel pump can increase the horsepower capacity of the engine. Additionally, the fuel injectors may need to be replaced or supplemented to support more power. It is also important to regularly change the fuel filter to ensure optimal fuel flow.

Adjusting the fuel pressure regulator

The right way involves modifying or replacing the stock fuel rails and using -AN fittings and braided lines. You will need to remove the stock FPR and set up a completely custom system. This method ensures that the fuel rail pressure is stable and prevents fuel starvation.

The second method is a workaround or a "hack way" to do it. This involves teeing the new FPR into the line after the secondary rail on the return side. Then, you need to remove the vacuum source from the stock FPR and plug it into the new FPR. However, the downside to this method is that the stock FPR will still be partially functional and will fight the new FPR, potentially causing issues.

Before making any adjustments to the fuel system, it is recommended to consider other factors such as the variable resistor, which can adjust the idle mixture, and an SAFC fuel controller, which allows for adjustments to the injector D/C over a range of driving conditions.

It is also important to note that the stock fueling system in the RX7 FC already has plenty of headroom, and adjusting the fuel pressure regulator might not provide significant gains without other modifications.

If you are planning to install an adjustable fuel pressure regulator, it is important to ensure that you have the correct indicators for the direction of fuel flow, as some regulators might not come with clear installation instructions.

Additionally, when adjusting the fuel pressure, it is crucial to have the appropriate tools to monitor the effects of your adjustments, such as a wideband O2 sensor, an EGT gauge, and logging software. This will help you understand how your adjustments are impacting the air-fuel ratio and make more informed decisions.

In conclusion, while it is possible to adjust the fuel pressure regulator in your RX7 FC, it is important to consider the potential drawbacks of the workaround method and ensure that you have the necessary tools and knowledge to make informed adjustments.

Checking/replacing brake and fuel lines

Checking and replacing brake and fuel lines is an essential part of maintaining your RX7 FC. Here are some detailed instructions to help you with this process:

Checking Brake and Fuel Lines:

• Begin by visually inspecting the lines for any signs of damage, such as flaking, rust, or pinholes. These issues can lead to leaks and need to be addressed promptly.
• Pay close attention to areas where the lines pass through tight spaces, such as the wheel well, as these areas are more susceptible to damage.
• If you notice any stains or signs of fluid leakage around the lines, this could indicate a parasitic leak, which requires immediate attention.

Replacing Brake Lines:

• If you find that your brake lines are damaged or leaking, replacement is necessary. Start by sourcing a new brake line that matches your RX7 FC. You can try finding a replacement line from Mazda, or you can purchase a prefabricated brake line from an automotive store.
• When you have the new line, measure the length of the old line and ensure the new one is equal to or longer than this measurement.
• Carefully bend the new line to match the shape of the old one, using bending tools or your hands. Be cautious not to kink the line, as this will require starting over with a new piece.
• Install the new line, ensuring all connections are secure.
• Once installed, bleed the brakes to remove any air and triple-check for leaks before driving.

Replacing Fuel Lines:

• For fuel lines, the process is similar. If you notice any damage or leaks, replacement is necessary. Source a new fuel line that is compatible with your RX7 FC.
• Measure the length of the old line and ensure the new line is of appropriate length.
• Bend the new line carefully to match the old one, avoiding kinks.
• Install the new fuel line, ensuring all connections are secure.
• Check for any leaks before starting the engine.

Remember, working on brake and fuel systems can be dangerous, so always exercise caution and refer to a professional mechanic if you are unsure about any part of the process.

Using a fuel pulsation dampener

The fuel pulsation dampener (FPD) on the 3rd Generation RX7 is prone to failure after around 60,000 miles, and this can cause fuel to leak from the fuel rails under the Upper Intake Manifold (UIM). This has been the cause of many engine fires and failures.

The diaphragm inside the FPD can tear, causing fuel to leak towards the rear of the engine on the passenger side. The fuel then puddles on top of the engine, next to the lower intake manifold, and can be ignited by the hot exhaust system. This can cause extensive damage, with repairs costing thousands of dollars.

There are a few options to address this issue:

• Replace the FPD with a new one, which costs around $130.
• Bypass the FPD, which can be done for around $2, but requires mechanical knowledge and experience removing fuel rails. This method involves tapping the primary fuel rail, cleaning it, and then applying Teflon tape to the threads of a 5/16 " Hose Barb x ¼ " (MIP Adapter) NPT fitting, and screwing it into the fuel rail.
• Convert to the more failure-resistant Kouki FC3S fuel rails (this option is only for Zenki FC3S owners).
• Completely eliminate the FPD by using a metric banjo bolt; this option is also only for Zenki FC3S models with the cast aluminum primary fuel rail and screw-on pulsation dampener.

Some people suggest that the FPD is an important component and should not be removed, as it was included by the manufacturer for a reason. However, others argue that aftermarket fuel systems often do not include FPDs, and that removing it can be done without adverse effects.

If you choose to remove the FPD, it is important to regularly check for fuel leaks, as a failure could have catastrophic consequences.

Upgrading the fuel pump

Choosing the Right Fuel Pump

Firstly, it is important to select a suitable fuel pump for your RX-7 FC. The stock fuel pump on the 2nd generation Turbo II RX-7 is designed to handle fuel requirements at near-stock levels. If you plan to increase fuel flow or modify your engine for higher performance, an upgraded fuel pump is necessary. Rotary Performance offers an upgraded stock replacement pump that is an easy bolt-in option and can support over 500 horsepower. This pump is manufactured by Denso in Japan and is known for its high flow rate and reliability.

Installation Process

The installation process for the upgraded fuel pump is straightforward and can be completed in less than an hour. It is designed as a direct bolt-in application, requiring no cutting, welding, or new lines. The kit includes all the necessary components, such as an OE inlet filter, o-rings, hose connections, hardware, and a ground wire for a wiring supplement.

Fuel Pressure Regulator

When upgrading the fuel pump, it is essential to consider the fuel pressure regulator. The stock fuel system on the RX-7 FC already has plenty of headroom. However, if you plan to increase fuel pressure or install a higher-pressure pump, you may need to adjust or replace the fuel pressure regulator to prevent overfilling the carburetors. Adjustable fuel pressure regulators are available, offering flexibility in fuel pressure settings.

Fuel Filter Maintenance

Maintaining a clean fuel filter is crucial to ensure optimal fuel flow and engine performance. It is recommended to change the fuel filter regularly, ideally every 24 months or 30,000 miles, to prevent debris from clogging injectors and impeding fuel flow. A clogged fuel filter can lead to reduced engine performance and potential damage.

Additional Considerations

When upgrading the fuel pump, it is important to consider the overall fuel system, including the injectors. The stock Turbo II fuel system uses two 550cc injectors for primaries and two 550cc injectors for secondaries. To support more power, additional injectors may be required. It is also essential to monitor fuel pressure and make adjustments as needed to ensure the system operates within safe limits.

Replacing the fuel filter

The fuel filter on a Mazda RX-7 is located between the car body and the differential. This makes it a challenging task, and you may want to leave it to a dealer.

Step-by-Step Guide

Prepare the Car:

• Start by releasing the fuel pressure. Open the gas cap to prevent pressure build-up in the fuel tank, which can cause fuel to be pushed out. It is recommended to have as little fuel in the tank as possible to minimize leaks.
• Jack up the car and secure it on jack stands. Place wheel chocks on the front tires for safety.

Access the Fuel Filter:

Slide under the car and remove the two floor pans on either side of the differential. One is black plastic, and the other is aluminum, secured with about five 10mm bolts. Removing both pans will provide better access and visibility.

Remove the Fuel Filter:

• Use a ratchet or an air ratchet with a 3-inch extension and a 10mm socket to reach the filter bracket bolts. Go between the gas tank and the suspension sub-frame.
• Remove the two 10mm filter bracket bolts, which will allow the filter to drop down slightly.
• Be ready to catch the fuel spill from the filter and the fuel lines.

Install the New Fuel Filter:

• Put the hoses and clamps on the new filter. This can be tricky, and it may be helpful to have an assistant hold the filter in place while you tighten the bracket bolts.
• Re-pressurize the fuel system to check for leaks and prevent the starter from grinding for too long.

Always wear gloves and eye protection when working with fuel lines, and cover yourself with a towel to catch any dripping fuel.

Frequently asked questions