[Phantom]

DonR you have it backwards if the O2 sensor is seeing extra air it will add fuel making it rich. Shutting the injectors off no fuel will be injected, if a controller is used it can simulate the correct O2 reading allowing for a switch to skew the results for the extra air. It would be easy to calibrate by running with all cylinders firing get an even reading shut off half see the change in O2 adjust then repete a few times till the change in O2 is ~1-2%.

(O2 mentioned above is not actual O2 but the reading the stock O2 sensor gives.)