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How A Fuel Pressure Regulator Works

August 31, 2022  -  Fuel, Carbs, & Intakes

16 People Found This Article Helpful

Building a fuel system requires careful planning and the right system components. The fuel regulator is an important part as it is responsible for providing the correct fuel pressure to either the carburetor or fuel injection system. It is important to understand the difference between a return-style and a returnless-style fuel system for both carbureted and fuel injected systems when planning and building your fuel system.  To help you with your research, we have provided the below answers to common questions about return and returnless fuel systems and regulators:

How A Fuel Pressure Regulator Works

A fuel pressure regulator with bypass is a component that controls fuel system pressure using a spring and diaphragm that is either adjustable or preset. Fuel from the fuel pump flows into the inlet and exits the outlet of the regulator to the carburetor or fuel injection system. Built into the diaphragm is a plug that rests in the bypass port below the set fuel pressure. When the set pressure is exceeded, the fuel pressure pushes against the diaphragm and spring, which lifts the plug out of the internal bypass port. This allows excess fuel into the bypass port to be routed back to the gas tank. Some bypass style fuel pressure regulator designs include a boost or vacuum reference, which provides additional pressure as vacuum drops or boost increases, to prevent fuel starvation under heavier acceleration.

What Is Not A Characteristic Of A Returnless Fuel System?

In carbureted applications, a returnless system does not circulate fuel back to the fuel tank with a return line. Fuel is pumped to the regulator, where pressure is reduced, and then continues to the carburetor, where flow is controlled by the floats and needle/seat assembly. With fuel-injected engines, a returnless fuel system does not have an external return line that brings fuel back to the fuel tank, directly from the external regulator or the fuel rails. Instead, fuel is recirculated inside the tank and pressure is controlled with an internal regulator, typically in factory fuel-injected vehicles.

How To Convert A Non Returnless Fuel System To A Return System

There are several ways to convert a non-returnless fuel system to a return fuel system, depending on how the fuel system is setup. For aftermarket and race applications, typically an external bypass fuel regulator is used, with a return line connecting it back to the top of the fuel tank. The (electric) fuel pump can be either inside the tank or outside the tank; mounted at or below the level of the bottom of the tank as close to it as possible. If using an aftermarket fuel injection, the fuel pressure regulator with return line can be mounted directly to one end of the fuel rail with the fuel supply on the other end or on the other fuel rail (in V6 & V8 applications for example) with the two fuel rails linked together. There are other ways to convert a non-return system to a return system, depending on if you have a factory setup or are putting aftermarket components together for a street rod or racecar. A JEGS expert is ready to answer your questions and help you build a return system for your application.

fuel system carburetor return regulator diagram holley

Where Is The Fuel Pressure Regulator Located On A Returnless Fuel System?

For factory fuel-injected vehicles, the pressure regulator is located inside the fuel tank on a returnless fuel system. In contrast, for return-style systems, the regulator is usually in the engine compartment near the fuel rails, with the return line from the rails or regulator routed back to the tank. In carburetor applications, the regulator is located in the engine compartment before the fuel filter and carburetor.

How To Hook Up A Carbureted Fuel Pressure Regulator With A Return Line

To connect a fuel pressure regulator with return line back to the fuel tank, the regulator needs to be a bypass regulator design. Next, connect the return line to the bypass fuel pressure regulator at the return or bypass port per the instructions, typically at the bottom. The other end of the return line connects to the top of the fuel tank. The feed from the gas tank enters the inlet of the regulator and exits to the carburetor fuel inlet to complete plumbing and installation.

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