When I turned the key on, with engine off and my fuel pressure goes to 38psi how long should this pressure hold? If I was to leave a gauge on it all night should the pressure be close to what it started at. I want to know if the check valve at the fuel pump is completely closed on a good pump, not allowing any fuel to seep back from the supply line. I am talking about a perfect system, no leaks at injectors, FPR etc...Thanks