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.
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.