cranks but won't start?

If it stays running when you add fuel, then everything signal wise is there, it's like its not firing the injectors when the ignition switch is in the crank position .
I would check at the injector connectors making sure they are getting pulsed , noid lights are handy for that . Or you can pull the injectors and rail to verify spray pattern in the cranking position.
Sounds very plausible it has no injector pulse in the crank position and does when you release the ignition switch to the run position.