88 Firebird with a TBI 305, was running before but now i cant get it to start.
It has a new ECM, distributor, fuel injectors, starter and battery, it cranks over very slowly, but stops cranking and makes a rapid clicking sound. I have spray from the injectors and should have spark because i have all new ignition parts.

 

Rapid clicking sound = bad connection at a battery cable or internal to the battery

Check your cables. Both ends of both cables. Make sure the black one is bolted securely to the block or whatever it goes to; make sure the red one is bolted securely to the starter. Take both of em loose from the batt and clean em by dunking in a solution of about 2 tablespoons of baking soda (sodium bicarbonate for all you chemists out there) in 6 oz of HOT (as near boiling as possible) water. Take a wire brush to the batt terminals themselves while the cables are off, and clean em up with a wire brush, then douse em with the baking soda solution and a paintbrush. Rinse everything thoroughly with clean fresh water (garden hose) and reassemble. You may find that one of your batt cables, or maybe even both, are bad, where the wire goes up into one of the ends. Replace if necessary,

 

checked all my grounds and they were terrible. started right up after