Hi! A year ago I replaced my NA pump in my NA 1993 300zx to a TT OEM pump. It ran amazing for three days and then the performance went back to the way it used to be (lacking). It used to make a super loud whining noise but now it’s basically silent. Whenever I turn off my car my fuel pressure drops from 39-42 at idle (when cold) to 20 pretty fast and then slowly drops to zero within a minute. IS THERE A CHECK VALVE ON A NA 300zx OR IN THE TT PUMP? I know there is a FPR check valve on the TT pumps that you can put on, but since this is on an NA I never hooked it up, and this wasn’t an issue that I was having before. Yes, I have replaced all injectors, the engine bays FPR and fuel dampener, fuel lines in the engine bay and I have inspected for fuel leaks all along the car, and nothing. When the car runs well there is no fuel smell at the carbon canister area, but when the car lacks in power the carbon canister does smell like fuel. Could this be a vapor valve issue? Is there a check valve in the pump or somewhere else? Sorry for the lengthy question, I have not been able to find one anywhere else.