Has anyone ever replaced or tested their check valve on the fuel pump?

My fuel lines do not hold any residual fuel pressure.. As soon as the fuel pump primes and turns off, the fuel pressure drops to zero. Here is what i've done so far to diagnose the issue.

1.) I've checked the injectors by having the rail off, and priming the fuel pump no leaks.
2.) I've replaced the FPR with a new AC Delco FPR
3.) I've checked the vacuum line going into the FPR to make that it does have vacuum.
4.) I don't smell or see any gas leaks around the car.

So the only thing it can leave is the check valve on the fuel pump. The fuel pump is a brand new 255 Walbro.

I have a trap door to get to the top of the fuel pump... I had a shop install it so I'm not very familiar the the set up.. Any advice would be much appreciated.

 

ive had a walbro 255 go bad on me same thing pressure would bleed off after it primed, repalced it with another one and a racetronix kit and its all good, i did the trap door mod and changed the fuel pump 2 times, its really not that hard if your somewhat mechanicly inclined

 

i have the same problem with mine. its really not that big of a deal, i just have to remember to hold the key forward for a second to let the fuel system prime before i start the car.

 

well it shouldnt do that. it is the check ball in the fuel pump. typically you would just plug off the return side to test if its the fpr or the pump (ofcourse or extrernal/inj. leaks too). its got a warranty, use it. course your labor wont be warranteed. but its very easy to do with a trap door.