I have moto 60s (IFR = 69.x lb/hr @ 58psi) and twin walbro GSS430s (one only active above 4psi).

My fuel pressure gauge reads 48psi on average at idle (whereas the mechanical gauge read 57psi when the motor was installed in Feb). The weird thing is that the idle fp ranges from 54psi through 46psi. Mostly the pressure is pretty consistent from start up (i.e. if it reads 48psi on start it is mostly 48psi at idle), but I will occasionally see weird events like a dip to 45psi every 25 seconds, and then a rebound to 48, etc. When the second pump kicks, the pressure goes up, so I'm pretty sure it isn't a plugged line or something, but am at wits end.

I need to somehow verify the voltage to the fuel pump, and I need to rule out a vacuum problem (have a few vac devices teed into the vac regulator line), but other than that am stumped.

No misfires, no overly rich running. Any ideas?

I did an MPG test today. On the highway at 12.1 AFR (was in open loop getting some VE logs) I got 9.5 mpg. My weekly average MPG is ~8 +/- .5 mpg. Note that tuning changes do not affect my mpg at all. (DFCO, running lean, lean cruise, etc. all produce the same numbers).

Could this be a leak? I never smell gas, but I wonder if it could be leaking at the tank, or if an injector is stuck partially open somehow (which doesn't seem plausible)