1993 Chevy Astro 1993 chevy astro doesn't start

I have a 1993 Chevy Astro van. Recently I changed the alternator and the fuel pump. The van has a throttle body injection system. The fuel injectors are not spraying when I try to start the van. I made it start once and suddenly while driving and stopping for a red light, it died and did not start again. Help me, what can be the cause of this problem. It looses some power whenever I press the brake pedal, or the engine seems to want to die when pressing it.