Ox sender actual function

Mark Wilcutts markw at vehicle.me.berkeley.edu
Wed Nov 25 18:52:11 GMT 1998


Maybe I shouldn't have posted only the first two pages.  With only part of
the paper, you don't get the whole picture.  The paper is actually quite
well written and makes it's points in a convincing fashion. They just
don't START with the assumption that the sensor senses oxygen. This
approach was needed because they were getting conflicting results from
their misfire tests. Comments below. 

On Tue, 24 Nov 1998, Orin Eman wrote:

> The first paper sets my BS detector off... as in the writers were
> completely clueless or they had some political agenda...

Do tell, what would that agenda be? If anything, they were annoyed because
they had been told by the manufacturers "this sensor senses oxygen", and
they found in their misfire tests that it didn't, as many of us have been
told, and are understandably annoyed. (For us it means we can't build our
own AFR sensor!)

I don't buy into conspiracy theories or "the gummint is just a big buncha
idiots". 

> <<However, very rich A/F ratios did not result in hIgh port sensor
> voltages when there was no ignition.>>
> 
> No surprise here either.  No ignition means 20% oxygen, same as
> on the other side of the sensor - so no voltage produced.
> The sensor really measures 'lack of oxygen' in the exhaust.

Ah, but where the surprise comes in is that at higher misfire rates, the
sensor indicates rich!

> <<These results indIcated that some physical property of the unburned
> air/fuel mlxtures, such as the relatively high  concentrations of
> hydrocarbons. or the absence of other types of reducing agents,
> such as hydrogen and carbon monoxide, inhibited the voltage generating
> capabilities of the sensors.  >>
> 
> Huh???  No mention of the simple fact that with no ignition, there
> is lots of _oxygen_ there...  Why no mention?  Why are they avoiding
> discussing what is generally thought to cause the low sensor voltage?

Beacuse higher misfire, e.g. more oxygen, and you get a rich reading...
they are taking a scientific approach - see how something behaves, then
match theories with it.




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