Vehicle Oxygen Sensors Question

[riffz]

So I'm doing a research project on Engine Control Units (ECUs), and I'm confused after reading this page:

http://auto.howstuffworks.com/fuel-injection5.htm

With parameter B as the level of oxygen in the exhaust, the lookup table for B is the point at which there is (according to engine designers) too much oxygen in the exhaust; and accordingly, the ECU cuts back on the fuel.

If there was too much oxygen in the exhaust, wouldn't you want more fuel to use it up, or decrease the air intake and leave the pulse width where it was? I just don't understand why you would cut back on the fuel if there was too much oxygen in the exhaust.

EDIT:
Nevermind, I understand now. (Don't feel like typing why)

 

[JBCM627]

Perhaps it means not enough of the fuel is reacting, and it doesn't want to waste fuel?