I have a 94 Pontiac firbird. After I changed my alternator the car cut on fine but once I put it in reverse the entire car cuts off everytime.
Not sure what you mean by "cut on fine"? Check all your electrical connections at the alternator, battery and starter. They must be clean and tight.
I'm pretty sure the alternator has nothing to do with your problem. it could be a sensor went bad. if the check engine light is on have your local part store do a check engine test on it to narrow it down. I'm thinking it is the mass air flow sensor or the throttle positioning sensor.
Search Pontiac Firebird Questions
Pontiac Firebird Experts