Originally Posted by Frank

We are having a couple of issues tuning the car. First we have abnormally high fuel pressure. We should have approx 50 psi and we have 70 psi.I suspect the new higher flowing pump is overwelming the factory pressure regulator and siphon plumbing driving the pressure up. The problem comes in when you get enough load on the fuel system the volume drops enough to let the regulator take over and hold pressure at 50 psi. The 20psi fuel pressure drop off is tough to tune a fuel map around. Its kind of like hitting a moving target. You chase your tail around, one minute its rich next its lean with no user input. I need to figure out what I need to do to get the pressure stabilized at 50 psi.

We also were getting air fuel ratios that would shift from one pull to the next. I have a G37 with stage 2 kit at the shop doing similar things with erratic a/f ratios and we found the bypass valve sticking. We have not performed the repair to confirm yet but I did verify the valve was not fully shutting at times causing large boost leak.
unfortunately yours is not so easy to get to to check in its current location behind bumper. I may need to check this if stabilizing the fuel pressure does not solve the erratic a/f ratios.