Fuel Pressure Regulator Assembly
WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The fuel pressure regulator is a vacuum operated diaphragm relief valve. The diaphragm has fuel pressure on one side and regulator spring pressure and intake manifold vacuum on the other side. The fuel pressure regulator compensates for changes in intake manifold vacuum by changing the fuel pressure. In this way, the fuel pressure regulator maintains a constant pressure differential across the fuel injectors under all operating conditions.