1994 Chevy Astro quits when accelerating

Engine Performance problem
1994 Chevy Astro 6 cyl Two Wheel Drive Automatic 248k miles

My beloved astro had recently begun to lose power when accelerating. I took it to my mechanic who could not diagnose the problem. The lack of power simply increased to the point of not even starting and idling. Here is what we do know:
1: There are no malfunction codes in the system, the computer reports that all is fine!
2: there is positive fuel pressure up to the injectors.
3: It will start on ether but immediately quit once the starter spray is gone.
In the distant past (within a year or so) I had 2 or 3 times tanked with bad gas that was resolved with some fuel cleaners. The symptoms were similiar but never JUST with accelerating.

a new symptom: I just went to lock it up. It had not been started for two days. I cranked it up and it ran for about one second and then no more such luck.


please help!