How does it work? I was wondering if it makes a difference where the sensor is located? On my engine it is in the drivers side exhaust, but I have seen them after the "y" pipe where it senses o2 from both heads. Wouldn't it matter in the prom calibration how much O2 it is sensing, either from 4 cylinders or all 8???

 

If there's a large variance in the mixture from worst case cylinder to best case cylinder, all 8 could cause the closed loop to oscillate too far, causing poor drivability/surging if it's in the Y. The distance from the engine also affects the loop time, because there's a delay from the engine to the sensor for the time it takes the exhaust to reach the sensor.

It doesn't measure the "quantity" of oxygen, just the "quality" or percent oxygen (not exactly, but just a way to get the thought across easiest). It could be looking at 1 cylinder or 100, and not know. Just looks at the mixture of the exhaust (amount of unburnt/unused oxygen). If it's seeing a high voltage (above 0.6V) the ECU will remove fuel from the fuel calculation when in Closed Loop only (not in PE, not with cold engine). If it sees a low voltage (below 0.3V) it'll add fuel to the fuel calculation.

It'll keep trying to get the O2 sensor to switch across those thresholds which keeps the Air Fuel Ratio at about 14.7:1, +/- 2% or so.