Pressure leakdown

[AZDatsun]

I am experiencing fuel pressure leak down in the rate of 36 psi to 0 in less than 10 seconds.  I have an aftermarket fuel pump so I put in a check valve right after the pump and now if I clamp the return line the pressure will not bleed down so the check valve is working.  As soon as I unclamp the return line the pressure drops to 0.  My pressure gauge is right after the front fuel filter before the rail starts.  I also disconnected my fuel rail and the injectors are not leaking. I also replaced my FPR and there are no leaks from that.   Any ideas why this is happening ? 

Edited May 5, 2022 by AZDatsun

[Zed Head]

Two leaky FPR's.  I had several at one time and found that most of them leaked.  The sealing surface is metal on metal.  Any rust or imperfections will allow it to leak.

I tore one apart quite a while ago.  The tube on the left is machined flat and seats on the flat surface on the right, with the round marks on it.  

One other possibility is that it's leaking through the diaphragm in to the intake manifold.  Pull the vacuum line and look for fuel.

[AZDatsun]

Well shoot I will put my old regulator back on and see if that helps.  It’s not leaking out of the vacuum line it’s already not connected as part of this testing and nothing from there.  If not I guess I will try a third regulator