The Fuel Pressure Regulator (FPR) in any modern car is quite a critical component of the fuel delivery system.
The purpose of the FPR is to ensure a constant fuel pressure that is higher than the intake manifold pressure. In most natural aspirated (NA) engines, the intake manifold maximum possible pressure is 1 bar, which is the atmospheric pressure of almost all places on earth. To ensure proper operations of the injectors, the fuel pressure must be higher than 1 bar, else air will enter the injectors instead of fuel exiting the injectors.
|Bosch's stock Fuel Pressure Regulator for W124|