engine starts and cuts off 2 seconds later

You've installed a new computer, coil pack, cam & crank sensor, fuel pump and all 6 injectors??? I'm sorry, but thought I heard of everything up to now. I guess not. Yes a plugged up cataylic converter can cause a engine to run.

I would suggest that you get a computer read out on your electronics. Could be a loose or broken vacume hose or disconnected wire that needs to be reconnected.