A fuel pressure regulator base has a fuel chamber adapted for plug-connection directly to the fuel rail to receive fuel from the rail, a flexible diaphragm closes the chamber, a cover forms a pressure chamber with the diaphragm, and the pressure regulator base further has a pressure passage adapted for plug-connection directly to the inlet manifold and extending to the pressure chamber to transfer the manifold pressure to the pressure chamber. The diaphragm thereby senses the difference between the fuel pressure and the manifold pressure and operates a valve to discharge excess fuel from the fuel chamber and the fuel rail and thus maintain the fuel in the rail at the desired pressure.