Date: Wed, 24 Nov 1999 15:38:35 -0500
Reply-To: Bulley <gmbulley@BULLEY-HEWLETT.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Bulley <gmbulley@BULLEY-HEWLETT.COM>
Subject: Re: How does the Oxy Sensor Work/ go bad?
From Oxygen Sensor Information
Written by Rick Kirchoff (rick@posms.cactus.org)
Edited to html by Jim Wright
http://atlantis.austin.apple.com/people.pages/Jimbo/o2info.html
Found by typing "How does an Oxygen sensor work?", into Altavista.
>>>>>>>>>>>>>>>>>>>>
An Oxygen sensor is a chemical generator. It is constantly making a
comparison between the Oxygen inside the exhaust manifold and air outside
the engine. If this comparison shows little or no Oxygen in the exhaust
manifold, a voltage is generated. The output of the sensor is usually
between 0 and 1.1 volts. All spark combustion engines need the proper air
fuel ratio to operate correctly. For gasoline this is 14.7 parts of air to
one part of fuel. When the engine has more fuel than needed, all available
Oxygen is consumed in the cylinder and gasses leaving through the exhaust
contain almost no Oxygen. This sends out a voltage greater than 0.45 volts.
If the engine is running lean, all fuel is burned, and the extra Oxygen
leaves the cylinder and flows into the exhaust. In this case, the sensor
voltage goes lower than 0.45 volts. Usually the output range seen seen is
0.2 to 0.7 volts.
The sensor does not begin to generate it's full output until it reaches
about 600 degrees F. Prior to this time the sensor is not conductive. It is
as if the circuit between the sensor and computer is not complete. The mid
point is about 0.45 volts. This is neither rich nor lean. A fully warm O2
sensor *will not spend any time at 0.45 volts*. In many cars, the computer
sends out a bias voltage of 0.45 through the O2 sensor wire. If the sensor
is not warm, or if the circuit is not complete, the computer picks up a
steady 0.45 volts. Since the computer knows this is an "illegal" value, it
judges the sensor to not be ready. It remains in open loop operation, and
uses all sensors except the O2 to determine fuel delivery. Any time an
engine is operated in open loop, it runs somewhat rich and makes more
exhaust emissions. This translates into lost power, poor fuel economy and
air pollution.
The O2 sensor is constantly in a state of transition between high and low
voltage. Manfucturers call this crossing of the 0.45 volt mark O2 cross
counts. The higher the number of O2 cross counts, the better the sensor and
other parts of the computer control system are working. It is important to
remember that the O2 sensor is comparing the amount of Oxygen inside and
outside the engine. If the outside of the sensor should become blocked, or
coated with oil, sound insulation, undercoating or antifreeze, (among other
things), this comparison is not possible.
>>>>>>>>>>>>>>>>>>>>>
Copied without permission
G. Matthew Bulley
Director
Bulley-Hewlett & Associates
www.bulley-hewlett.com
Cary, NC USA
888.468.4880 tollfree
-----Original Message-----
From: Mark Keller [SMTP:kelphoto@ISLANDNET.COM]
Sent: Wednesday, November 24, 1999 1:44 PM
To: vanagon@GERRY.VANAGON.COM
Subject: How does the Oxy Sensor Work/ go bad?
Greetings,
Can someone tell me how the Oxygen sensor actually works. Does is work
by actually sensing oxygen in the exhaust? Or does it "correlate" by
providing exhaust temperature to the ECU, which then interprets the
Oxygen based on other inputs from the injection system.
Does water or methanol in the fuel cause the oxygen sensor to read to
rich or lean?
Does water or methanol, or other fuel additives, cause an oxygen sensor
to fail prematurely?
Sincerely,
Mark Keller
91 Carat "Lazarus"
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