Low Fuel Pressure w/ Backup Pump On

I see and hear about this all the time on low wing aircraft and the RV12. No one seems to have an actual engine issue with the pressure fluctuation.

Thanks for the info, Roger.  Any ideas though about WHY it happens?  I'm just curious as to what's going on.

I have to get back to the airplane and verify the part number (which it turns out is stamped on the mounting flange not the pump body) and plumbing but I don't believe this Facet pump has a check valve and is installed in the fuel line with no line bypassing it if that's what you meant.  I'm thinking when it's shut off, the fuel just continues to flow through it but I'll verify that.

Ya, the standard installation has a bypass to the electric fuel pump(s).  See diagram.

If yours does not have this, it might well explain the issue.  Without knowing anything about your particular pump, it has to be at least somewhat restrictive for fuel to be flowing through, instead of around, a stopped electric pump.

Thanks, Tyler.  So if that turns out to be the case, then does it make sense that fuel pressure is lower with the Facet pump turned on and higher with it turned off?  I get back with you once I take a look at the installation.