So I installed a Holley adjustable fuel pressure regulator on my 90 efi 460. From the articles I have read, everyone says to set it at 41 psi. Does this mean 41 psi at an idle with vacuum line connected? Or disconnected? Or 41 psi at wot with vacuum line connected? I can't seem to find any info on it. I am currently running it at 41 psi at idle with the vacuum line connected, and it runs good with better power, but I don't want to screw it up.

 

It baffles me why anybody would put an adjustable fuel pressure regulator on unless they are running a carburetor.

The fuel injectors need 39.2psi across them at all times for maximum fuel burn. That is what our era V8 Ford trucks are set to with a factory fuel pressure regulator.

A fuel gauge at the fuel rail will be from 30psi to 42psi depending on the V8 engines vacuum/pressure. This is to maintain the 39.2psi fuel pressure across the injector.

The ones who told you 41psi that would be with no vacuum (engine not running) with the fuel pumps running.

 

Engine can be running, but only idle with no vacuum, and set it to 39-41 for the factory spec. With vacuum connected it will lower the pressure.

Why did you add this regulator.
I have used an adjustable regulator to help a lean condition in the upper rpm range of my 460. Mine just liked the extra fuel.