My little bro. has a diprocol fuel pressure guage that seems to be a little off. When we first installed it we found fp too low. So off to the dealer. After they changed the lift pump it guage was still reading low. Took it back to the dealer and they said that guage was reading 5 or so psi low. Now it moves erraticly at idle. It doesnt ever stay at a constant psi. Any ideas.

 

Try another gauge? Maybe something in the line to the gauge causing it to read erraticly? That happened to me on a fuel pressure gauge on a turbocharged Mazda Miata...