1989 GMC S15 truck won't run

Engine Mechanical problem
1989 GMC S15 4 cyl Two Wheel Drive Manual

I have a 1989 GMC S15 2.5 engine that won't run until I poor gas in the throttelbody. I have checked the fuel pump, and it checks ok. I have checked for fire to the fuel injecter and it's ok. I have already put a new computer on it. What else can be wrong with it? Why won't it run?