1990 montero died while driving at 60 mph.?

trying to figure out why my montero doesn't run anymore. i had put in a rebuilt ecm prior to this to get it running originally, then i was driving and it died completely, and was actig like the ecm isn't there anymore..... ie.... not check engine light, and when i connect to the diagnostic port on the vehicle it acts like computer is bad, but when i sent it in under warranty for repair they said the computer is 100% ok. I hav e checked the ignition module, and the coil, it has a new distributor, plugs, plug wires etc.... i get spark up to the coil. but not beyond when i crfank over engine. if you have any ideas this would be appreciated because both me and my mechanic are stumped.