Date: Fri, 7 Aug 1998 09:43:09 -0500
Reply-To: Darrell Boehler <midwesty@TAOS.MIDWEST.NET>
Sender: Vanagon Mailing List <Vanagon@vanagon.com>
From: Darrell Boehler <midwesty@TAOS.MIDWEST.NET>
Subject: oxygen sensor
Content-Type: text/plain; charset="iso-8859-1"
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Hi again Michael,
Thanks much for sharing your knowledge with us. You seem to indicate
the number of times a minute the mixture changes rich to lean or oxygen
sensor voltage goes above and below 0.5 volts is a pretty good indication
of how healthy the oxygen sensor is. I will do some testing and request
others on the list observe the number of fluctuations per minute and try to
establish a norm. This may be some good information and maybe we can see
an oxygen sensor starting to deteriorate and get it replaced before it fails
completely. Please have someone else drive while you are watching the LCD
meter or do it in the drive way volks.
Darrell
>Darrel, a CO reading between .3 to 1.1 with the O2 sensor connected still
wont
>tell you the condition of the actual O2 sensor. The only true way to find
out
>the condition of the O2 sensor, is to monitor how quickly the voltage
>fluctuates, high to low, the swing rate of the voltage and how tight. New
>VW's since 1996 with OBD2, the engine ECU is constantly monitoring the
voltage
>fluctuations, response time and how tight the swing is. If at any time the
ECU
>doesn't see this, the ECU will store a fault and turn the check engine
light
>on. It can happen with a new car with only 10K on it, I see it all the
time.
>OBD2 is so wonderfull because it monitors everything, and I can watch it
all
>on a VW computer. Now that your vanagon doesn't have OBD2, you need to use
>your wonderfull volt meter. With a hot motor, dissconnect the O2 sensor and
>get a voltage reading, watch it carefully, analog voltmeter would be best,
so
>you can see how quickly and how tight the swing is of the voltage. The
swing
>rate should be within a second, from a high to low voltage. Turn your
mixture
>screw counterclockwise, LEAN, your voltage will be low, around .1 (100
>millivolts). Now turn it clockwise, your voltage will go up to .9 (900
>millivolts). .5 is perfect air fuel mixture, you'll see on your digital
>voltmeter a high of .7 and a low of .2, fluctuating rapidly up and down,
>sometimes you'll see .5 in there. What matters is, that it is an average of
.5
>volts. An analog volt meter would be better ( unless you digital meter has
an
>anlalog graph). If you were to check the CO now it would say probably .6
CO,
>that is a little too lean for a vanagon. That setting is what it will be on
a
>cold start up, wich is too lean for a vanagon. Keep in mind that the ECU
>isn't looking at your O2 sensor voltage until the engine reaches a certain
>tempurature. Per temp sensor, the ECU will then take O2 sensor voltage and
>then adjust accordingly. The purpose of setting the voltage higher is for
>cold run characteristics ONLY. The ECU will always keep adjusting the
amount
>of fuel to the injectors so it will see an AVERAGE of .5 volts. Swing by
a
>dealer or independent VW shop and hook it to the CO machine, along with a
volt
>meter and see for yourself. Have fun. I'd like to know how it turns out.
>Michael Modl.
> 87 syncro
> 87 quattro
>
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