I don’t normally struggle much with these motors. This one is going to put me in the nut house. Kept popping relays. Parked it for a while hoping to find time to fix the problem. Now the damn thing won’t start. Fuel pump works, disconnected fuel pump module, took apart although it stated not to. Changed o-ring and cleaned. Put back together. Not getting fuel pressure to the rails but both relays are working and can get the motor to crank by priming the bulb but this appears to be from the overflow vent fuel flowing into the throttle body. Fuel rails will not prime.

What do I not understand about fuel injection based on my explanation, what should I be doing next to figure out what the heck is wrong with this thing. Doesn’t appear to be electrical.

Should there be a shreider valve that will allow the air out and fuel rails to prime?

There is no schrader valve, they will burp on their own. Poss no pressure from the hi press pump..

Hopefully some others will chime in but possibly the wiring harness? I know you say you don't think it's electrical but that fixed my problem. New wiring harness and I was good to go.