When I was working on troubleshooting and fixing my fuel line issues I noticed that when first starting my RJ502, it cranks for a while before it will start. I turn the key on, let the fuel pump shut off (about 5 seconds), and then immediately crank it. The fuel pressure goes to 55-60 PSI (don't remember exactly) with the key on, and stays there while running. However, when I shut down the engine the fuel pressure drops pretty fast. Shouldn't it hold fuel pressure when off?

I assume this pressure drop is caused by either a leaky injector(s), a leaky fuel pressure regulator, or a bad pump check valve. All parts are new but I know that doesn't mean much . I can hear fuel returning to the tank when I shut the engine off, so I assume it's a bad check valve in the pump causing the pressure loss, however, I think a leaky regulator could cause that as well. I wonder if leaky injector(s) are causing the engine to have too much fuel in the cylinders and only cranking clears it out. I'm not sure how to isolate the pressure drop.

The pump is an in-tank Walbro 255LPH high pressure model and the fuel rail is a GM part, a common single fuel rail for all 8 injectors that was also used on the ~2000 8.1L Vortec engines. The regulator is at the back of the fuel rail and bypasses fuel back to the tank and is a common regulator used on many GM engines.

How big of a deal is this pressure loss? What else could cause the excessive cranking?