I installed a piston fuel pump and an isspro fuel pressure gauge about a year ago and all was fine fuel pressure was about 14 psi and held pretty steady. Now the needle on the gauge flops around banging off the pins. Do I have a bummed gauge or is something else wrong. Truck runs fine.

 

if it's the ev2 electrical one its probably the sender.
i had this problem & i went through 2 senders. (warrentied though)

 

If You don't have a snubber (sp?) You might want to give that a try.