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From this example, you can see how the control system makes adjustments. 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. http://www.howstuffworks.com


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Now, on the last sentence where it says where there is too much oxygen in the exhaust; and accordingly, the ECU cuts back on the fuel. I think this statement is incorrect, it shoud say something like if there is too much oxygen in the exhaust then the ECU will add more fuel.

If the combustion process isnt using all oxygen, then more fuel should be added to go with the oxygen not being used. The only situation i can think of where you would want to cut back on fuel is if you were running extremely rich and combustion could not occur because the spark plugs are fouled or something. The misfire monitor would detect the unequal powerpulses and go into limp mode of something. Is howstuffworks wrong or do i have it messed up?