The actuation/functionality of the fpr solenoid should be visible on your fuel pressure gauge.
The fpr solenoid is commanded by the ecu and affects the fuel pressure by venting the vaccuum signal to the fuel pressure regulator coming from the intake manifold to atmosphere. It only operates during hot starts.
It's a little confusing, but if you think it through, you'll see how it works.
The fuel pressure regulator uses intake manifold pressure to vary the fuel pressure to match engine operating conditions.
At low manifold pressures, you get lower fuel pressures.
At higher manifold pressures, you'll get higher fuel pressures.
When you're cranking the engine over on the starter, (with the throttle closed) you'll be drawing a vaccuum inside the intake manifold.
The fpr will decrease the fuel pressure in this situation.
Those wily engineers figured out that increasing the fuel pressure during the crank mode with a hot engine would help hot restarts.
They achieved this by using the ecu to command the fpr solenoid to vent the fpr reference signal from the intake to atmosphere on hot restarts.
This means instead of the actual vaccuum in the intake, the fpr will "see" one atmosphere, (ambient barometric pressure) and that will increase the fuel pressure ~5 psi (ish).
This is the same fuel pressure you would have with the vaccuum hose to the intake removed from the fpr, and the engine idling... or key on/engine off ... as both of those situations have the fpr "seeing" atmospheric pressure.
If you eyeball your running fuel pressure with the engine hot and then shut the engine down for a few minutes, apon cranking/restart it should read ~5psi higher than it it did idling.
After a minute or two, the ecu will release the solenoid, the true vaccum signal from the intake will resume at the fpr and your fuel pressure will drop back to ~36psi.
Hope that helps, I'm not much good at explaining things like this /ubbthreads/images/graemlins/blush.gif