My 2004 f550 started having hard starts yesterday about mid day when temps were in the mid 50's. No warning just hard to start. Took about 10-15 sec to fire up, then vroom. Any possible suggestions as to what might be happening?

 

Have your batteries load tested. Then test the FICM. https://www.dieselbombers.com/ford-p...procedure.html

If the FICM is bad, let me know, I can fix them.

When you're cranking the truck over, is there any smoke coming out of the exhaust?