Well I just rebuilt my 1988 rx7 t2 and tried to start it for the first time and noticed the fuel pump isn't running and the injectors aren't opening up. What would cause this?

 

Did you remember to reconnect the main ECU ground to the engine?

And plug in the EGI relay if unplugged? Also check the EGI fuse.

 

just to let you know that the fuel pump does not turn on when the key is in the ON position,..it turns on at START,then by rolling the engine over the AFM sucks enough air and kicks a relay to keep the pump running.
So you need to make sure that the EGI fuses are good and the AFM is plugged into the Harness.