If anyone is pulling out their hair on this one I finally figured it out if you wanna know the answer to this riddle its one of two things 1.your nuetral safety switch which is in the middle if the console under your shift plate on center console or 2. In my case it was the intake air temperature switch which is located on the front of your engine block right next to where your thermostat housing is located ...on my camaros 305 TBI and 350 tpi this little sensor tells the ecm the temp of the engine air and or coolant of the engine if faulty it will not allow your engine to start it will crank all day but won't start replace it and tell me if this solves your problem took me 3 months of replacing this and that to finally figure it out been working in 3rd gens since I was 18 now 34 I'm not a novice at this rebuilt 6 3rd gens so far and am always able to answer any of your questions or troubles you may have