Manuellabour247

When you rev it, it opens the injectors to allow more fuel for the engine. More flow = less pressure. Not sure it should drop that low. You can get a variable fuel pump, but there's really no reason to unless you're building this engine for racing.

Chris_1

iTrader: (1)

Fuel pressure regulator is just a vacuum valve. Idle or coasting with your foot off the gas creates vacuum and opens the fpr, allowing some of the fuel to go back to the tank, decreasing fuel pressure and creating a "softer" spray pattern from the injectors.
Something about how your fuel system is operating is not right.
Remove and replace the vacuum line to the fpr while idling and see what happens. Pressure should increase when you remove the vacuum line and decrease again when you plug it back in.
If that doesn't happen your fpr is faulty. Also check that vacuum line for fuel smell. If the vac line smells like fuel, the diaphragm inside the fpr is leaking fuel into the intake through that line.

Chris_1

iTrader: (1)

Go back to my first post about the gauge. Key on engine off you should see 42.
When you start the truck and it's idling, you have high vacuum, the fuel pressure regulator (fpr) should be open and your pressure should drop by 5 to 8 psi.
Opening the throttle a bit decreases vacuum, which should cause the fpr to close and cause fuel pressure to rise back up to 42 -ish.