Checking rail pressure while cranking

[Konstantin]

Ok, I changed lift pump and removed and cleaned anti drain back valve. I installed used lift pump from another truck with dead engine. Now my problem disappeared. I know Rawze told to wait 10-15 seconds and that is what I will do , but for the sake of experiment I tried to start truck right up and it starts every time. So i guess my problem is solved. But I run into another one. I connected a gauge to check what pressure lift pump gives. When I first turn ignition gauge reads around 13 psi. What happens next is kind of weird, after some time like 30-50 seconds pressure suddenly changes to 0 and stays there. Pump is working 2 minutes. If i disconnect it and connect it pumps 12 psi, but after some time drops to 0 once again. The noise is also changing when pump pumps 12 psi and pumps 0. Is it normal? Or I did something wrong? Quickserve says I need to install new gasket, but mine looked pretty good, so I reused old one.