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Old 11-14-2012, 11:05 PM   #23
the suicidal eggroll
Scooby Guru
Member#: 51961
Join Date: Jan 2004
Chapter/Region: RMIC
Location: Broomfield, CO
2005 STi
2012 WRX


Originally Posted by shin1 View Post
My wideband reads very close to the stock O2 sensor near the stoich area, but as the AFR gets richer (below 13), the reading between the two becomes further and further apart.
The wideband always reads leaner and in the low 12's, the wb is leaner by as much as 0.8 compared to stock .. is this normal? (my stock O2 doesn't go below 11.36 so not sure how big the gap is below that).

I'm about to scale MAF based on the wideband readings, but I'm worried I could be making it too rich, if my wb's reading is wrong. Should I trust the wb?
That's due to the pressure in the uppipe, as has been said a few times in this thread. The way the wideband sensors work depends heavily on the pressure of the air that they're measuring. Raise the pressure, and it alters the readings. The pressure in the uppipe pre-turbo is very high, IIRC it's roughly twice as high as the intake manifold pressure, and this causes the stock sensor to read rich when in boost. Install your wideband post-turbo, or move the stock sensor post-turbo, and the problem disappears because the pressure there is more or less atmo.
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