Oh, in regards to the high pressure keeping the injector from opening, either the pressure is doing it, or the ECU senses the high pressure and prevents the injector from opening. If the injectors were opening it would instantly relieve that high pressure in the line, but it doesn't. With that check-valve installed the pressure, as measured with the OBDII tool, stays up around 55-60 PSI. In that condition I can crank the engine for 15 minutes and it will never start, or even cough. However, as soon as I relieve the pressure by pressing in on the Shrader valve, the car will start instantly. Either the pressure is mechanically preventing the injectors from opening, or the computer is telling them not to open. I think it is more likely a mechanical thing because I get no errors or codes. The Injectors are probably made so that under pressure they seal the injector opening. That prevents them from leaking fuel when they aren't supposed to. The very high pressure is so high that the solenoid can't pull the injector open. That's just my guess.

Is it possible to remove the fuel line from the fuel rail at the engine and plug it with a schrader valve and see if the pressure is dropping from the tank? At that point you can identify what is related between the tank to the Schrader valve or related to the fuel rail. It ma narrow it down for you. You would need a pressure valve to connect. All of this may be related to your fuel pump not providing the instant pressure.

Does that seem like correct behavior? I thought the ECU was supposed to be smart enough to run the pump for however long it took to achieve the correct pressure in the fuel rail for starting.

(Also, your noodling on the injectors not opening at high pressure seems inescapable to me.)