I just started my LQ4 conversion with a Walbro 255 pump, 3/8" plumbing, and a corvette FPR. I flip the pump on and I immediately get 58psi at the fuel rails, but when I start the car, after about 5 or 6 seconds the idle slows down, stumbles, and eventually cuts out with the fuel rail pressure dipping down to about 30psi.

Anyone have any idea what might be causing this? Is it possible that the learning process of the engine is making the injectors dump so much fuel at first that the pressure is dropping that much? I know for sure that the pump is working and providing enough gas.

 

As long as that pump is running and your regulator is functioning properly there's no way it should drop anywhere near 30 at an idle....

If it's slowly losing pressure as it idles i'd check these things...

Pump is getting power "as car is running"
Pressure regulator is working ok.
Sock on bottom of fuel pump is plugged or sucking something to the bottom of the pump causing it to not be able to supply fuel.

Good luck.