Re: how to tell if O2 sensor is Bad...

[T Berk <tberk@mindspring.com>]

(Dave? Uh, um no.)

Ahem, <cough, cough>

OK, here we go!

Found at: <http://www.scuderiaciriani.com/rx7/O2_sensor.html>
(Don'tcha just love Google :)

From: Rob Robinette 

How the O2 Sensor Works 

The oxygen sensor detects oxygen in the exhaust in a way similar to a
battery cell. Platinum layers on the inside and outside of the probe act
as electrodes. Zirconium dioxide between the layers of platinum acts as
an electrolyte. The inside layer of platinum is exposed to the air in
the engine bay, the outer layer is exposed to the exhaust. When the O2
sensor is hot it generates positive voltage between the two layers of
platinum. Negatively charged oxygen ions in the exhaust are attracted to
the platinum and reduce the voltage that the Engine Control Unit and
air/fuel gauge reads. 

That's why a rich mixture = higher voltage from the sensor (more gas =
fewer negative O2 ions to drop the voltage) . Just remember "L=L", Lean
= Low voltage. You can attach a Volt Ohm meter (black to ground, red to
the O2 sensor) to monitor your engine's air/fuel ratio. Full throttle
with 0.82 volts is best performance but slightly higher voltage (richer)
is safe. At part throttle the ECU will bounce the ratio from rich to
lean. You only have to worry about full throttle. I suggest you have a
copilot read the voltage while you accelerate at full throttle. 

The 3 wire sensors are used to give power and ground to pre-heat the
sensor so it starts working quicker, it has no effect after the sensor
gets warmed up. 

==========  Note: These readings given are in specific context to Mazda
RX-7s.======  Lets get some VW specs in here.

from the A2 GTI list archives:
<http://veedub.nu/a2_16v/archive/1999/May/0147.html> 

AND Jan's FAQ Web Site! WooHoo!
<http://lipari.usc.edu/~jan/vw/Engine/lambda.html>
<http://lipari.usc.edu/~jan/vw/Engine/ExhaustAnalyzer>

TB: So, the O2 doesn't get it's supply of air down the wire, it's a lot
easier than that. You _should_ avoid crimping, (Brett, I'm not an EE,
but I play one on T.V.*) Soldering and a suitable shrink wrap or other
covering is the way to go. You want to avoid creating any additional
load along the signal path, you want to avoid degradation in the future
due to oxidation and corrosion. Plus this is why a leaky, cracked gasket
or exhaust manifold will through off your mixture.
Thems me thinks. But wait! There's More!
And this is my last word:
<http://lipari.usc.edu/~jan/vw/Engine/oxysensor.html>

hth,
TBerk

*Pops worked on many things when I was young, including the Electron Gun
Trigger at S.L.A.C, but me- I never got my General Ed credits together.
:( But, I have something on the wall from Hard Knocks U. Int. :]

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