Ok, I've been having a miss/stumble/backfire problem lately. The fuel pump is a month old 255 lph, new plugs, wires are ok, all coils are firing (LTCC). Anyhow, I checked the pressure today and here's what I got.

Key on 38 -40 PSI

Running 40 PSI

Running w/regulator unplugged 43-44 PSI

Now when I started it and it was cold, the pressure was dead on 40 PSI no movement from the needle. As the car warmed up and I revved it a time or two, the needle would start wobbling between 38-42 PSI very rapidly. I'm wondering if this is normal or if I need to look at replacing the regulator.

 

Bump for the night crew.

 

The fuel pressure regulator increases absolute fuel pressure as manifold absolute pressure increases with throttle opening. The realative fuel pressure should be constant (about 44psi - 300kPa)