As far as diesels go 6.9's are stone simple and
very reliable in my experience.
But I have met a few that don't want to start without a shot of juice.
I have a friend with an '88 dually that was this way. Chasing our tail with new injectors and such.... 🙄
Try putting the key on and plugging/unplugging the solenoid rapidly.
Listen closely.
It may be that it is stuck or failing, and the rattling from a running engine is enough to get it to open.
But if the fuel system had a bunch of rust in it that's a nightmare no matter how many filters you change.
Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.