1990 g20 van unknown fuel delivery issue

[Chevy13luv]

Ok, hi, yes I am a novice at these forums, and Ive been learning as i go when working on behicles. So, my husband and I have a client (mobile mechanics i guess u can say) who has a 90s g20 conversion van. It has the 5.7 l motor, the 700r tranny, pretty much your basic 2wd3/4 ton silverado. Anyways, the owner had let it sit for 3 years then decided to try anx start it. Without dropping the tank and removing the now varnished gas. He said it ran for a couple mins, then died and couldnt get it to start again. Enter us. We dropped the tank, cleaned the lines (they were some heavy duty upgraded metal ones and client was on a budget), rebuilt the tbi, i replaced the spring in the fuel pressure sensor, we also replaced the ivnition control module, the oil pressure relay, the fuel pump relay, the fuel pump itself, and im sure im forgetting something but anyways, van wont start. Has spark. And fuel pressure is at 13psi. We have power everywhere except at the injectors, which are not spraying. We replaced the injectors and the wire connectors as well. And are stumped. The only other thing we are suspicious of is that there are a bunch of after market wires underneath the steering column, which are for some alarm system. Maybe they could be keeping the tbi from working and subsequently not allowing the van to start? Either way we need to figure this out or we dont get paid and all those hours of time wasted. Thank you so much and i apologize for any mispelled words, im doing all this on a mobile phone.