What is a Fuel Pressure Regulator?

Mary McMahon
Mary McMahon

A fuel pressure regulator (FPR) is a device which is designed to keep the pressure in the fuel lines of a vehicle consistent. It is located between the fuel source and the engine, along the fuel rail, the line which carries fuel to the engine. This device is critical to the smooth functioning of an engine, as fluctuations in pressure can cause a variety of problems. To determine whether or not the fuel pressure regulator is working properly, a test can be performed to determine the fuel pressure; correct fuel pressure ranges vary, depending on the vehicle, and they are often listed in the owner's manual.

A fuel pressure regulator is critical to the smooth functioning of an engine, as fluctuations in pressure can cause a variety of problems.
A fuel pressure regulator is critical to the smooth functioning of an engine, as fluctuations in pressure can cause a variety of problems.

If the fuel pressure is too high, it can cause an engine to run rich. This increases the emissions from the vehicle, and it can cause clogging, racing, misfiring, and a variety of other problems. Low pressure makes the engine run lean, in which case the engine may take a long time to start, if it starts at all, and it may misfire, hesitate, or halt. Both of these circumstances are highly undesirable, and the FPR prevents them from happening.

This device can sense the pressure in the fuel rail, and modify it with a flap which can be opened or closed to decrease or increase pressure. If the pressure becomes extremely high, a valve opens to allow fuel to flow into a line which leads back to the fuel tank. A number of things can influence fuel pressure, including leaks in the line and problems with the fuel pressure regulator.

If a car's gas efficiency radically declines, it has trouble passing emissions tests, or its engine is running irregularly, it can indicate a problem with the fuel system, and the FPR is an easy thing to test. A mechanic can usually test the device in a few minutes, determining whether it is working properly or not. If the fuel pressure regulator is working, additional diagnostic tests will be needed to track down the problem.

Having an engine which runs poorly is not just annoying. It also increases vehicle emissions, which is bad for the environment, and it is hard on the engine. An engine's life may be shortened if it is consistently run with the wrong fuel pressure, leading to potentially costly repairs or a catastrophic failure in the future. If an engine starts to run rough, it's time to make an appointment with a mechanic, or to take a look under the hood, for the mechanically-inclined.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


Mechanics are not that good at finding sources of problems. These days they just plug the car into the diagnostic machine and take the readings as gospel, then they will change a load of sensors which half the time don't fix the problem. They can't really be called mechanics -- fitters is a better word. And all for £90 an hour. It's a pure rip off. Mechanics are a lost art.


The fuel pressure regulator can have its interior spring weakened because of time and use, and thus regulates fuel slower and imprecisely, which will strain the fuel pump which will then run hotter and hotter until the pump can only pump the minimal amount of PSI of fuel while the regulator goes out completely. The now weakened pump is running at a much lower psi than it should and the car will still run but will cut out and misfire either often or intermittently. It's hard to diagnose but easy to fix. The solution: replace the fuel pressure regulator and the fuel pump and all the mysterious problems will go away. I know this from a lot of personal experience.


I have a GSI 20SEH engine, and all of the symptoms that targets the FPR failure. I took a look at it and what I saw was a little hose (about two inches long) that connects the FPR with the fuel railing (holding the injectors) that looked like it's about to burst. It was like a small balloon. I don't know -- is that normal?

P.S. The car wasn't driven for about a year.


I had a related, but different, problem in my old car. The fuel pump pressure regulator worked, but the gas gauge on the dashboard did not. It would tell me I had space for about a quarter of a tank more of gas, even when I filled it to the top. I at least don't think i was a pressure issue, because the car still ran with the same efficiency, it just meant I had to keep a tally in my head of how much fuel I had left.


If the fuel pressure regulator in a car stops working, it can be really difficult to know things like how much gas you have, as well as damaging the engine as is mentioned here. Thankfully, mechanics are usually pretty good at being able to find the source of the problem.

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