Ford F81Z-9C968-AB Fuel Pressure Regulator

EFI models maintain constant fuel pressure from the fuel pressure regulator by causing resistance beyond the injectors, thus allowing some of it to go back to the tank. It can vary its restriction through engine vacuum, a diaphragm, and a spring as engine requirements change. Additionally, when the fuel pump is not running, the restrictor closes very fast and acts like a check valve thereby aiding quick engine restarts. For proper functioning, fuel flow should be unblocked, an open return path must exist along with a dependable vacuum signal. Failure can result in overpressure or underpressure which are caused by contamination or valve malfunctions.