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Old 05-10-2012, 05:52 PM   #10
the suicidal eggroll
Scooby Guru
Member#: 51961
Join Date: Jan 2004
Chapter/Region: RMIC
Location: Broomfield, CO
2005 STi
2012 WRX


Most likely explanation is a bad MAF scaling. Boost pressure does not affect fueling in a MAF-based system (unless of course the higher boost pressure causes you to saturate the MAF or the injectors, or puts you into an untuned region of the MAF, but that's a separate issue).

Remember, MAF doesn't care about boost boost pressure, MAF only cares about air flow. If what you said was true, it would be impossible to control fueling properly using a MAF. Just think about near redline. Once you pass about 5000 RPM, boost starts tapering, and flow doesn't change much. The MAF reads about the same, while boost drops from say 18 psi to say 14 psi. If the fueling system depended on boost pressure like you're suggesting, you would be screwed. Luckily, it doesn't.

Take your setup. You're implying that you changed the MAF scaling due to the higher boost. What happens if you let off the throttle slightly, so you're not running the WOT 18 psi anymore, you're running 11 psi at partial throttle. Does your car swing ridiculously lean? It shouldn't, if it does then there's something very wrong with your tune, and has nothing to do with the FPR.
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