On Oxygen Sensors
 

Reposted from rec.autos.tech:

Note: I do not vouch for the accuracy of the content, although as far as being accurate on a basic level, I believe this is correct. Either way, it's interesting.

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Ok, let's try this again. I'm looking for information as
to how to interpret O2 content in the exhaust. Here's what
I've got so far:

Here's what I know so far:

An O2 sensor is basically a zirconia/oxygen battery, it generates a
voltage depending on the O2 content, the voltage being generated by
the difference in O2 content between the exhaust stream and the
outside air, the zirconia is exposed to outside air as well as
the exhaust.

A normal O2 sensor is not linear, in other words the voltage
output is not proportional to the amount of O2. In fact, it is
so non-linear that a regular (narrowband) O2 sensor is used more
as a switch to sense rich and lean than it is actual O2 concent.

The computer senses the voltage from the O2 sensor, above or
below 450mV, and drives the mixture to the opposite, rich or
lean, this causes the sensor to switch, and then the computer
drives the mixture back in the other direction. The constant
switching back and forth from lean to rich is referred to as
crosscounts, and the computer makes adjustments to the mixture
so that the average voltage is 450mV from the O2 sensor.

A wideband O2 sensor is designed to measure actual O2 content,
rather than function as a rich/lean switch. It does this using
a variety of techniques. Sensor temperature has a strong effect
on the voltage output of the sensor, so WBO2 sensors are heated,
with temperature sensors and variable-rate heating elements so
that the computer can keep the sensor at a specific temperature
regardless of the exhaust temperature. Because the voltage output
isn't linear with O2 content the computer is programmed to interpret
the voltage output and deduce the actual O2 content.

Excess O2 can be in the exhaust for several different reasons:

1. False O2 from a break or defect in the exhaust system ahead
of the O2 sensor allowing outside air to be drawn in.

2. Lean mixture having O2 left over from combustion after all
of the fuel was consumed.

3. Misfire resulting in unburned fuel and O2 being sent into the
exhaust system. The O2 sensor sees the O2 even though the mixture
may be just right on other cylinders, or on cylinders when no
misfire is present.

Interesting stuff... sorry I missed it until now.