1989 F-250 5.8L FI
I know that the fuel pressure regulator usually fails because of a busted diaphragm, but can it just become weak?

My fuel pressure is sitting at about 27psi at idle. It goes up a few psi when I pull the vacuum line. I clamped my return line at the tank and the fuel pressure fluctuated between 80psi and 100psi. BTW, the truck ran and idled great at the high pressure.

The symptoms I currently have are low pressure at the fuel test port, rough idle, slight stumble while accelerating. I have replaced my in-tank low pressure pump, replaced fuel filters, repaired kinked lines. I have bypassed the frame mounted dual function reservoir for the time being.

 

remember its a fuel pressure regulator. did you check the pressure when you kick it during a crank key on engine off rest pressure. how a bout a MIL try pulling codes and the only thing the line crimp will do is flood the engine

 

Yes they wear out. It's a spring and a needle valve. Could also have some debris on the seat causing low pressure.
They are cheap. Just buy a new one. Idle pressure with vacuum disconnected should be 39-42 or so. Vacuum connected will lower it some.