1993 Chevy Astro 1993 Fuel System Problems

I am trying to fix my Mother's 1993 Chevy Astro van. The fuel filter, fuel pump, relay, injector, and computer have all been replaced with new parts. The van will run for about 10 seconds when gas is poured in, but cuts right off. Otherwise, it will not turn over or run at all. It does try to turn over. What else could it be? Please help-in desperate need. Thanks so much.