Fuel Pressure Regulator

What is a Fuel Pressure Regulator?

Aeromotive Fuel Pressure Regulator (Fuel Rail Mount)
Aeromotive Fuel Pressure Regulator (Fuel Rail Mount)

As the name implies, a fuel pressure regulator (FPR) is responsible for regulating the pressure of fuel flowing through your vehicles system. It is used to maintain a steady fuel supply, even during dramatic changes in fuel demand. Different engine operating conditions will require different amounts of fuel, such as low or high RPMs. This is where the fuel pressure is doing its job; adapting the fuel supply to the fuel demand. For your vehicle to achieve successful fuel and air mixture, proper fuel pressure is required in all situations.

How does it work?

A fuel pressure regulator is found virtually in all internal combustion engines. Without it, your fuel rail will not be able to build up enough pressure to support the injectors. Without the sufficient amount of fuel, the fuel will instead flow straight through and not reach the injectors.

How a FPR Works
How a FPR Works

Your fuel injectors have two sides. One side of the injector is under pressure from the fuel rail, and the other side is air boosted by a turbo or a compressor.The ideal ratio is 1:1. The fuel pressure regulator regulates the fuel pressure against the air pressure/boos., This leads to that the fuel injector can maintain the perfect ratio between fuel and boost.

Your fuel pressure regulator consists of a diaphragm that controls the bypass valve “ball seat” it can open and close in order to adjust itself for a steady fuel delivery. When pressure (boost) is applied to the top of the regulator, the diaphragm, which is attached to the bypass valve, a spring forces the diaphragm down and reduces the amount of excess fuel. This makes the fuel pumps work harder while the fuel pressure increases linearly towards the increasing boost pressure from the intake manifold.

Performance Fuel Pressure Regulators

AEM Adjustable Fuel Pressure Regulator
AEM Adjustable Fuel Pressure Regulator

Your factory fuel pressure is designed to work with a factory fuel system. If you upgraded your vehicles performance and fueling system its important to install a proper FPR. Larger injectors, forced induction, a high volume fuel pump, and other mods can easily deem your OE regulator useless.  Your factory regulator cannot be adjusted to increase your new needs. Luckily, there are performance FPR on the market that allow you to adjust your pressure so you can reach peak performance.   Additionally, many manufactures offer fuel pressure regulators that are produced for every type of fuel system and level of modifications.

Holley Fuel Pressure Regulator (EFI)
Holley Fuel Pressure Regulator (EFI)

Some fuel pressure regulators use vacuum operated mechanical diaphragms to change pressure.  However, there are vehicles that are equipped with an electronic FPR. Both styles can be found from various manufacturers. Some fuel pressure regulators are built directly into your fuel pump assembly. However, most fuel pressure regulators are mounted in the fuel rail. When entering the market for a new FPR, It’s important to know its location, as well as if it is electric or mechanical.

Carbureted Systems

Just as fuel pressure and volume are critical for EFI engines, so is maintaining the fuel level in the float bowls on carbureted engines. Your carbureted system may also require a fuel pressure regulator. While these engines operate at much less fuel pressure, if you’re modified you may be pushing your factory fuel pressure regulator to the limit. Carbureted systems operate typically around 6 psi, which stock fuel pumps are designed to deliver fuel at this pressure. However, if you install a larger mixer or multiple carbs, fuel volume will become necessary. Electric fuel pumps and even high-volume mechanical pumps generally deliver fuel at pressure that is too high for carburetors to handle, and so a fuel pressure regulator is needed.

Signs of a Failing Fuel Pressure Regulator

Your fuel pressure regulator plays a direct role in the distribution of fuel to your engine. Any issues with it can cause performance issues, as well as some other problems. There are several signs you can look out for when it comes to failure.

Misfire & Performance Issues

One of the first signs we usually notice when our FPR begins to fail would be performance issues. This component as we explained controls the fuel pressure, and when failing will throw off your engines air fuel ratio (AFR). This alone can dramatically affect the performance of your vehicle. If you would like to monitor your air fuel ratio, installing an AFR gauge is extremely beneficial. You may also experience misfires, reduced power, a drop-in fuel efficiency, and reduced acceleration. These types of vehicle symptoms can occur from other problems wo whenever your vehicle is misfiring, losing power, or bad AFR its important to bring it into your mechanic for proper diagnosis.  

Fuel leaks

Another symptom of a failing fuel pressure regulator is fuel leaks. If the fuel pressure regulator’s diaphragm, or any of the seals fail, fuel leaks can occur. A faulty regulator can not only leak gasoline, but can also cause performance issues as well. A fuel leak will usually produce a noticeable fuel smell. Since your fuel is not getting where it needs to go, you will experience performance issues as a result.

Black exhaust smoke

If you have black smoking exiting from your exhaust, we’ve got a problem! This is another sign of your FPR failing. If the fuel pressure regulator leaks or fails internally, it may cause the vehicle to emit black smoke from exhaust system. A faulty fuel pressure regulator can cause the vehicle to run excessively rich, which apart from reducing mpg and performance, can cause the vehicle to produce the black smoke. Since black smoke can be caused from other issues, it’s important to get your vehicle checked by a mechanic immediately for proper diagnosis.  

In Conclusion

It’s important to keep the proper fuel running throughout your system. When one component is failing, or mismatched (factory/modified) your hard work is at jeopardy. We don’t modify our vehicles to lose power, we want gains! Your performance fuel pressure regulator will make sure your system receives the right amount of fuel to keep getting you those gains!

Several manufacturers that offer performance fuel pressure regulators include:

Aem Eletronics


BD Diesel Performance