The fuel system diagram provides a simplified view on how fuel flows within an EFI system. The fuel tank supplies gasoline to the fuel pump. The fuel pump can be located in the fuel tank or external to the tank. The fuel pump provides a high pressure feed to the fuel rail that contains the fuel injectors. On the fuel rail there is a pressure regulator that limits the fuel pressure to 39-45 PSI and maintains a constant pressure. The pressure regulator has a vacuum line that connects it to the intake manifold. Any excess fuel leaves the pressure regulator and is returned to the fuel tank.