1985 volvo 760 Turbo will not start

[lock7man]

1985 760 turbo automatic, jetronic 4 cylynder

symptons: started to lose performance over weeks
went to get gas - filled tank - went dead - rolled it a few feet - it
started fine. in all cases engine rotates freely

wx got real cold - would not start - then cranked for many minutes
and it finally coughed and got it started - did add some dry gas

now it is dead. wont start but it roates. will cough periodically. measured fuel pressure ~80 psi, good compression, injectors work OK
spark at the plugs exist (not sure how strong)
cleaned and regapped plugs - car started like it was new - for 5 seconds.

could be fuel quality ?
could be air - is there a way to check?
could be ignition - this has the EZ11k
computer ?

I have a spare vehicle for parts.
Any assistance in diagonosing would be appreciated.

thank you.