Checking for leaking fuel injectors
 

So as part of my troubleshooting of a loss of fuel pressure, (primes to to 40+ PSI and holds that while running but drops to about 10 PSI imediately after shut down) I pulled the fuel rails and injectors and put paper under them, primed the engine and all the injectors gave a quick spray on the first turn of the key.

Is that normal for a cold start? After that I could keep priming and nothing sprays. Then I let it sit and noticed no leaks after an hour and pressure is still at 10psi.

First off...what year Vette...??

I'm not sure if that is normal injector behavior but it sounds as though the FP problem lies elsewhere, i.e. in the FP or FPR.

To test the FPR clamp the fuel return line above the tank and power the pump on/off. If pressure holds, replace the FPR.

To test the FP power the pump and clamp the delivery line. If pressue holds service/replace the pump.

Clamp off your return line, see what happens. If pressure holds, it's a bad regulator. If pressure still drops, it's the check valve in the fuel pump. Confirm that by crimping off the pressure line, when charged.

How does ^that test isolate fuel leak down point?