Fuel Pressure Regulators

The fuel pressure in an electronic fuel injected engine must be within a specific range, to ensure there is an ample supply of fuel available to the fuel injectors for all engine operating conditions. The fuel injectors are electro-mechanical devices controlled by the PCM (Powertrain Control Module). One terminal on the injector is connected to 12V. When the PCM grounds the other terminal, the coil in the injector raises a plunger, allowing fuel to spray.

The electric fuel pump delivers fuel to the fuel rail at a constant pressure, and the fuel rail mounted injectors spray fuel into the intake ports. The PCM varies the pulse width, the time the injectors are grounded, to suit engine load. The pulse width is shorter at idle, and lengthened when the engine is under load and more fuel is needed. But without a means to regulate pressure, there could be too much pressure at idle, and not enough at wide open throttle.

The fuel pressure regulator maintains fuel pressure within the specified range. It is mounted to the fuel rail and contains a spring and a diaphragm. A port connects the regulator to engine vacuum and it is also connected to the fuel return line, which allows fuel to flow back to the tank. At idle, when less fuel is required, engine vacuum acts against the spring and diaphragm to allow excess fuel to flow back to the tank. When the throttle is opened and more fuel is needed, the reduced vacuum under such conditions allows the spring and diaphragm to restrict return flow, ensuring there is enough pressure for the increased pulse width.

A fuel pressure regulator will typically fail closed, resulting in too much fuel pressure, a rich mixture, poor fuel economy and excessive emissions. If you disconnect the vacuum hose from the regulator and the fuel pressure doesn’t rise, the regulator is most likely faulty. However, there could be a problem with the vacuum signal, caused by a cut or broken vacuum line, so to be sure, apply vacuum with a hand-held vacuum pump. Fuel pressure should drop as vacuum is increased. If it doesn’t, verify that the return line isn’t blocked, and if not, replace the regulator.

However, if the spring in the regulator breaks or the regulator leaks, this will result in fuel pressure that is too low and a lean condition. If fuel pressure is low and doesn’t rise when the fuel return line is pinched shut, the fuel pump is most likely at fault. However, if the pressure does rise, the regulator should be replaced. Regardless of the failure mode, we have the replacement fuel pressure regulator to restore proper engine operation. All of the regulators we offer are manufactured to OE specs to meet the specific fuel pressure requirements of each vehicle, and ensure ease of fitment and perfect engine performance.