2000 CTD, no mods, the mechanical fuel pressure gauge used to be rock steady and hold 12psi at idle and 5 or 6 at WOT. Now it bounces around and drops to 3 at WOT while only holding 8 or 9 at idle. I replaced the fuel filter, lift pump and put in high flow banjos with no changes. Is there a fuel sock on the tank pickup that could be clogging or is it something with this crap diesel fuel available today? I can't find good ole' no 2 diesel anymore.....

 

Do you run fuel all the way to the gauge or are you using an isolator? If using an isolator maybe air has gotten into the glycol. Even if running fuel all the way to the gauge could air have gotten into the gauge line? You could hook up another gauge under the hood and compare gauges to see if the problem is indication or a real problem.

 

i would try what busboy said, hook up a test guage to the vp44 test port and see how it compares to your gauge in the truck, that would tell you if its a gauge problem or something with the fuel system..