351W SEFI - Fuel Pressure loss after shutdown

I recently completed my SEFI swap on a 351W (see thread in Bronco chat). I noticed that after the truck sits for a while, it takes two attempts to start it. First attempt it will start but then stall, second attempt it starts right away. Sounded like a fuel issue and this is what I found out.

Fuel pressure at idle is 34psi. If I remove the vacuum line from the regulator, it jumps up to 40psi. Once I shut the engine off, I left the pressure guage attached (to the schrader valve on the rail) and the pressure slowly bled down to below 20psi before I pulled the guage. I think it bleeds all the way down to 0 pressure if I let it sit long enough. This would cause the starting issue.

How can you tell if it is a regulator issue or a injector? All my injectors are firing (I can hear the clicking on each one when tested with a long metal rod).

I have the 96 Explorer fuel rails and 24lb injectors. Both were purchased used but where in very good shape and clean.

I am leaning toward the regulator being bad but wanted to get some opinions before I send the $$ on a new one. If I have to get a new one, would an adjustable be worth the money?

Thanks. Bill

I'd lean towards injectors might want to check your plugs. The regulator sounds like its working correctly from your test. I would think that when you turn the key on the fuel pump would pressurize the system and it would start right up but of course if you turn the key all the way to start it may not have had enough time to pressurize the rail and the extra fuel from leaky injectors foul the plugs on the first try. On your second try the fuel rail is pressureized and the excess fuel has been pushed out the exhuast. Or I could be totally wrong as I'm no injection expert

Do you have the Probst EFI book? If so it tells how to test to see if it is the injectors, pressure regulator, or fuel pump. All three can cause this. Have you run an RPM drop test on the injectors? I know you said they are all working but are they actually opening and closing right? The rpm drop test will tell if they are. Don't recall offhand how to get the test to start but the Probst book also goes over that as well. If I recall right you hit the throttle within 30 seconds of the self test completing to get it to start but I would need to eithr try it or look in the book to see. (Don't have the book handy right now or I would look up both for you)