Could really use some help

[gc73]

All right so i checked fuel pressure. 15 PSI key on while pump is running. when pump shuts off pressure falls to about 5 PSI maybe little under. When the motor is running it gets up to about 15 and flutters a little around that 15 mark. I pulled return line off the fuel pressure regulator and am getting NO fuel through the regulator at all.

I did replace the fuel pump right at a year ago with a GMB 520-1021 Electronic Fuel Injection Pump. https://www.amazon.com/gp/product/B00D44...UTF8&psc=1 Is a link to the pump that i bought and installed.

Why would pressure fall off as soon as the pump shuts down? Pressure Falls off immediately and sharply not like a slow leak down from 15 to 5. It is nearly an instant drop. shouldn't the system hold pressure or is it back flowing through the pump. I have no leaks anywhere else in the system that i can find. Would sure think that a leak this substantial would be pretty easy to spot after cycling the pump a dozen or more times.

Thanks for the help!