The only time the pcm is using the O2 for fueling is anytime your O2's are bouncing. Anytime you are in PE your pcm is not using the O2 to calculate fueling. That is how I understand it. I could be wrong though.

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Red 2dr 99 GTP: Z7 t66, A/A IC'd, Custom Heads, 65# Inj, ST2 Cam, Meziere Elec Pump, JP Double Roller(with machined crank gear), Plogs, PLX W/B, Powrtuner

99 Regal GS (work car)