I installed a manual fuel pressure gauge about a month ago and it has been working great until earlier this week when I started off to work I noticed the gauge was pegged out all the way and stays there until the truck is shut off, any ideas, could it be as simple as air in the line or something.

 

15 psi gauge or a 30 psi gauge?

 

I had this very same problem with my guages two different times. both times it was a bad sending unit for the guage. vp44's destroy sending units without an isolator.