Date: Sat, 3 Feb 2001 01:28:11 -0600
Reply-To: Larry Alofs <lalofs@ENTERACT.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Larry Alofs <lalofs@ENTERACT.COM>
Subject: Re: O2 Sensor Voltage
Content-Type: text/plain; charset=us-ascii
kenneth d lewis wrote:
> Mark;
> It should oscillate up and down, eventually very quickly as the
> engine heats up runs faster. Below is some text on the sensor.
> On my web site there is a picture of a gadget I made to monitor
> the O2 output. Check it out.
>
> Drive Safely & Good Luck
> Ken Lewis <Kernersville,NC
> 86 VW crewcab;60 356B Coupe
> Go to neksiwel.20m.com for pictures of my cars and some Vanagon tech
> stuff.
>
> Diagnosing Oxygen Sensors:
>
> The oxygen sensor is really a simple device : It tells the engine
> computer how much O2 (oxygen) is left in the exhaust . With this
> information the computer can determine the best air/fuel ratio ;
> stoichiometry.
>
> When the O2 sensor detects too little oxygen in the exhaust it tells the
> computer the engine is running rich (please send less fuel).On the other
> hand too much O2 means a lean mixture (please send more fuel).
>
> The O2 sensor kind of acts like a fuel cell(a battery is a good analogy).
> A voltage is produced (1 to 1.5 volts) when there is a difference of
> oxygen levels between the inside of the sensor(the environment air) and
> the outside of the sensor sitting in the exhaust stream . This indicates
> a rich condition or to little O2.When there is O2 in the exhaust (lean),
> the inside and outside of the sensor has less O2 differences and the
> voltage output drops to zero.
>
> BUT the sensor must reach operating temperature to work(real hot) i.e.
> the computer ignores any input from sensors on a cold engine. This is
> known as "open loop operation",the computer wings it.After the sensor
> heats up the computer goes into "closed loop operation".The sensor
> detects a lean mixture then the computer allows more fuel from the
> injectors. This produces a rich mixture,sensor voltage drops,computer
> leans out the mixture.An endless cycle. In other words the mixture never
> stabilizes at perfect but continuously toggles around it.
>
> If you have a good voltmeter you should see this voltage swing from a
> fully heated operational sensor.
>
> You can test your system with a 1.5 volt flashlight battery. Disconnect
> the sensor lead. This is easiest deduce with a single wire sensor. Three
> wire sensors have two wires for a heater, DON'T mess with these.Connect
> the negative side of the battery to chassis ground. touch the sensor wire
> going to the computer to the positive side of the battery.This fools the
> computer in thinking there is a rich mixture present. It attempts to
> correct by leaning out the mixture ,hopefully making the RPM's drop.The
> output of the sensor should drop also.
>
> On the other hand if you ground the sensor lead going to the computer it
> thinks the there is a lean mixture and attempts to compensate by send
> more fuel hence the engine SHOULD surge. At this time the output of the
> sensor should climb.
>
> On Thu, 1 Feb 2001 19:12:44 -0600 Mark Ingalls <ingalls_mark@HOTMAIL.COM>
> writes:
> >Hello Volks,
> >
> >With my Digitool on my 85 Digijet, my O2 reading at idle goes from
> >.75ish to
> >.1ish or less then back up to say .8ish.
> >
> >This goes on many times a second.
> >
> >Is this the normal cycling, or should it be smoother and stay around
> >say .4
> >to .6?
> >
> >Mark Ingalls
> >0 degreesF in Nebraska and testing my just constructed digitool.
> >_________________________________________________________________
> >Get your FREE download of MSN Explorer at http://explorer.msn.com
>
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Ken,
Can you share more details about your O2 sensor monitor?
I have found the voltage difficult to follow with a digital meter because
it changes so rapidly. Analog meters usually have too low an input impedance
and change the circuit voltage significantly.
Larry A.
Chicago
91 GL
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