Why won't my 99 firebird start?

My 99 pontiac firebird cranks
but won't start. New pump,
sounds good when turns on.
Got fuel all the way to fuel
rail. Spark is good. Relays
are all good. No codes, no
lights on (check engine or
security lights). Spray starter
fluid down throttle body and
starts up and purrs till runs
out of fluid. Seems like the
injectors aren't opening.
What would cause this, and
guys there ain't much I
haven't went threw for this
problem. Other then. The
basic checks????? I'm about
ready to pull my hair out.