when  we  had   350 chevy-olds-buick  (ya  what ever lol)    diesels we had that problem all the time.

the way  it was set up  you  THOUGHT  you had the air out  but  didnt.

the way we finally got to doing it was  ONE  injector at a time and not all at once---  and of course   MAKING SURE    NO air was left in that  rossa-master pump...  which was  a   CHORE  on its own   since it sat  down  inside the  V  in an place that caught  air.