Checking rail pressure while cranking

[Konstantin]

Hello, I want to check for rail pressure while cranking. I was told it has to be at least 100 psi. I do not know how to check it. I connected 100 psi gauge in rail compucheck fitting. The problem is while I crank the truck fires in about 6-8 seconds and I can not identify pressure when cranking. And with truck at idle pressure is 250 psi. Somebody told me to disconnect shut off solenoid, but with shut off solenoid rail pressure stays at 0. Any advice what could I do?