A fuel pressure regulator is a device designed to maintain a constant fuel pressure in your engine. How does it work? Well, the fuel pressure is maintained because inside the regulator housing there is a spring pushing against a diaphragm, the spring pressure has been pre-set for the desired fuel pressure. If your fuel pressure regulator is damaged, you will notice a lack of fuel pressure, excessive fuel pressure, black smoke and rich engine running condition, instant drop of fuel pressure once the vehicle has been turned off and a delay building sufficient fuel pressure. Features: Fully adjustable from 25psi - 75psi. Uses Original Bosch Regulator! Bolt-in - No Modifications Needed