Fuel pressure reading unstable

[DMAN302]

Hey wondering if someone can help me out with some info here.
Yesterday I had my bad boy out for a run when I noticed my fuel pressure gauge was reading 37-39 lbs while driving light or heavy or at a stop just idleing, then later ( about 5-10 minutes later)the pressure would drop back to low near 30 at idle???? the Idle is strong and steady so why would I have 38-39 psi at idle with engine at normal operating temp? Fuel gauge is a phantom autometer, and I will note that when I pull the vac line of the intake from my stock fuel regulator the Idle will raise up and the pressure on the gauge reads a solid 39 psi vac off. Is it normal to pull 38-39psi pressure just sitting there at idle..or is my regulator acting up?

 

[85 Coupe 5.0]

The pressure should jump about 5 to 9 LBS when you unplug the regulator. Idle Fuel pressure should be around 35 or so? maybe someone can chime in with a spec. But, reguardless, it should go down about 5 to 9 LBS when you apply vacuum to the regulator and go back up when you take it off. Since you have an in-car guage, it should jump up under acceleration and go back down upon letting up on the gas pedel.

 

[DMAN302]

Yes it should but the pressure is hanging high wether I'm at idle or under acceleration I find the gauge will fall back to 30-35# most often, but sitting at a light 38-39# seems too high..like I said vacume off the idle will come up a bit and the needle will jump to the proper pressure of 39 which is factory spec. Question is about my reading at idle with vac on..I know what vac off should do. Thanks for the imput though I do apreciate it.

 

[85 Coupe 5.0]

ok, so stock is 39 PSI, under WOT conditions. Sooooo, at idle you should see 32 to 35 PSI. As long as you don't have an adjustable regulator. Is there any fuel coming out from where the vacuum line goes into the regulator? Sounds to me like the regulator is on it's way out, but it's hard to tell without a little more testing.