Instant fuel pressure loss
 

I have a 1992 Chevy Corsica with the 3.1L motor in it. I use this car as a figure 8 car, so the stock tank is removed, but I have a 5 gallon steel tank in the rear with an external fuel pump hooked to a toggle switch. When I put a fuel pressure gauge on the rail, it reads about 47 pounds of pressure with the needle having some quick small vibration back and forth. When I put my vacuum gauge on the fuel pressure regulator and pump it up, I can control the pressure and drop it as mush as about 10 pounds, and when I do so, the vibration stops and it holds steady.
I have noticed that when I shut off the pump, the fuel pressure instantly goes down to 0. From what I understand, the fuel pressure should hold pretty steady even after shutting down the pump. The car will sputter a little when cranking over, but won't really start and stay running. Could this issue with the fuel pressure cause this to happen, and what could be causing it? I have also removed the vacuum lines from the intake, and plugged two of the ports, and run the other port to the fuel regulator and MAP sensor. Is there any other vacuums that need hooked up for proper motor operation? I tried jumping the diagnostic port on the OBD1 port and it only flashes code 12, so surprisingly there are no error codes on the car. Any help would be greatly appreciated!

You need to install a check valve in the fuel line. This will hold the pressure when the pump is not running. The factory fuel pump assemblies have a check valve built into them.

This is it, unless your pressure regulator is not working right...