I'm installing a SD TPI unit and installed a new bosch pump at the same time. When the fuel pump runs with key on, the pressure goes to 45 psi. Once the pump shuts off after 2 seconds, the pressure drops to 0 in 5 seconds. I pinched off the rubber return line, and when the pump runs, it goes to 70psi and holds once the pump shuts off. Lost maybe 3 psi over 15 minutes of off time. Seems to be the regulator. I replaced the diaphragm with a delco unit and have the same pressure loss problems. Could the problem be the seat in the regulator? It seems smooth but has a weird coloration in one spot.

 

The hardened disc and seat are lapped to a fine surface finish. I'd suspect the FPR leaking, too.

 

hmmmm I did this same test last year, so i replaced FPR with a ac delco, same problem, so I then got a adjustable one, same problem, pressure drops to 0 after key off instantly

 

https://www.thirdgen.org/forums/tpi/...fuel-pump.html

 

so leaky injector, that would be a lot of gas leaking out, im thinking more in the pump

can i install a inline check valve on the return line?

 

Follow up:

I replaced the whole regulator with another one I got off ebay. No more pressure loss. I even tried with my old diaphragm and it still holds pressure. Must have been that seat that was leaking.

 

Good deai!