2014 CTS-V Sedan A6
So I was able to flash my FPCM without paying extra - I guess HP Tuners took pity on me, or I managed to make enough revisions to my tune over the years that I unlocked a bonus level!
Anyway, I finally got rid of my CEL from the Dsteck Aux pump. @adam112 ran a dedicated relay when he helped me install his amazing fuel hat, and I got the CEL every time I hit boost for a Fuel pump secondary circuit low voltage due to the relay (P0231). Although I disabled the code and even FPCM reporting altogether in the ECM, the code would persist - the FPCM has many of these codes duplicated onboard, and only when I disabled the FPCM DTC reporting did the CEL finally disappear!
It also looks like JAustin's fuel pressure tweaks bought me a little extra headroom on the supply side - so far it looks like the rail pressure dip that's commonly reported has been minimized. The dip is still there, just not nearly as severe. I suspect there is more to here as my FP starts to ramp back up at higher RPM but I'm not quite sure what to change. It probably has something to do with one of the fuel flow rate vs voltage tables (or similar).
Fun fact: with the 9.55 / 3.0 pulley ratio, I'm hitting almost 19psi in 65*F ambient. yay!
Have you changed out the pressure relief valve in the fuel pump basket? That little fucker opens up at 68'ish PSI. Tom and I are about to change ours out so we don't have FP issues at the track this spring. Trying to find a weekend to knock them out.