On my claret 92, when I turn the key to on,(engine not started) the fuel pressure goes up to 35 psi, and after 10 seconds it drops off to 3 psi.
(I attribute that to a leaking fuel injector.)
With the engine running, and 14.3 volts being pumped out by the alternator, the psi stays at 39-40 at idle.
SVXRide has a inline gauge on his 92, lets check his out.
Note;
When I first installed my adjustable fpr, the pressure would stay up for hours with the engine off.