My mate has put 3 digital oil pressure guages (different brands) in his FG xr6 turbo and while the car is cruising the guage fluctuates between 30 and 90 psi he has moved the guage sender from the T piece to a sandwich plate on the oil filter and that has stabilised the reading at idle but not cruising . We must be missing something cause all 3 guages he has had have done the same thing
He is now using a drift guage