Fuel Pressure Regulator Assembly
WARNING: This page is about a different car, the 2005 Saturn L300. However, it is still accessible from the selected car via links, so may be relevant.
The fuel pressure regulator is a diaphragm relief valve. The diaphragm has fuel pressure on one side and regulator spring pressure on the other side. Fuel pressure is controlled by a pressure balance across the regulator. The fuel system pressure is constant. A software bias compensates the injector on-time based on the signal from the MAP sensor.