Fuel Pressure drops to zero as soon as ignition turned off...91 Q

[Locknut]

Well I finally got my fuel pressure gauge and quess what....my pressure drops to zero immediately after the car is shut off. The fuel pump was replaced two years ago. Could it be the fuel pump backflow check valve? The fuel pressure regulator? A bad injector o ring wouldn't bleed that fast would it? The car runs fine once I turn it over long enough to start.

[Q45tech]

There are flat pliers without serrations designed to clap off hoses without eating into them.

Check which way the drain is occurring: 1. block off return line and turn off?

Block off line after filter and turn off......................if it isn't going out one of the hoses [leading off engine], Guess where the fuel is going [besides an under plenum fuel hose leak on to plenum].

[Locknut]

Thanks Q45tech...I pinched off the supply from the filter to the rail and now mysteriously I have 40lbs pressure back in the line on shutdown. Could pinching off the supply line while the car was running have activated a faulty pressure regulator....I noticed there was something on the passenger side fuel rail that looks like a regulator as well...leading back to the fuel tank? Could this have been stuck open....circulating the gas right back to the tank?