Hey everyone, have a question about how the FPR works. I got a code 45, turns out I have leaking injectors. But part of that was to test the FPR. (No fuel in the vacuum line so I'm pretty sure it was OK.)

Key on engine off, pressure was 42.5. I pulled 10" vacuum with a Mityvac on the FPR. Pressure lowered by 4 PSI. When I released the vacuum, pressure went back to the original value! The pump wasn't running- I didn't expect pressure to go back up. I did the same with 23" vacuum- pressure dropped with vacuum, then went back up when I released the vacuum.

Doesn't pulling a vacuum on the FPR mean the valve is opened, which compresses teh FPR spring, which uncaps the fuel return port under the FPR valve? So shouldn't all of my fuel have whooshed down that return port when I applied vacuum? Or is the vacuum not strong enough to overcome the FPR spring?

I know my FPR isn't stuck b/c pressure doesn't go higher than 42.5 (clamping off the return line put pressure at 59 psi, releasing the return line = "whoosh" pressure dropped to 42.5.)

Thanks!