ihdude

iTrader: (1)

Just installed FAST fuel rails with a Holley fuel pressure regulator 12-846. I set the regulator to 58 psi at idle and took the truck for a spin. Checked gauge after I drove it and it showed 52 psi. I don't see or feel any fuel leaks. What is causing the pressure to drop after driving it?

DynOmite

If you readjust it to 58 will it hold ?

ihdude

iTrader: (1)

The first time it dropped to 55 psi so I bumped it back up to 58 but had a fuel leak. Fixed the fuel leak and it held 58 while I let it idle for several minutes. Held 58. Drove it about 5 miles and filled up with gas. Checked the gauge and it ran 52. Is there a break in for the diaphragm and spring? Should I set it back to 58 again or is something else going on?

DynOmite

Boost or N/A , and are you running a vac or boost reference line to the regulator ?

ihdude

iTrader: (1)

N/A. Using a vacuum reference.

DynOmite

My experience is with oem/factory stuff , and carb FP regulators in the performance world , but just asking the basic questions , maybe someone with experience with this unit will have an answer ..

What is the Fuel pressure showing with pump running engine off vs engine running ..

Or what's the fuel pressure with the engine idling then adding and removing the vac line ?

I looked up the instructions for the regulator but didn't see when it said what the standard fuel pressure drop was when adding vacuum .. or rise with no vacuum

Blah blah blah , lol , free bump anyhow , haha

DynOmite

Or the old "tap lightly on the regulator , see if something is sticking in it " diaphragm styles sometimes take a few adjustments to get one that holds proper .. wouldn't think that would be the case here , just thinking aloud

joecar

BTW: did you set rail pressure to 58 psi with the vacuum hose disconnected...?