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Date:         Wed, 24 Aug 2011 23:08:14 -0400
Reply-To:     Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject:      Re: O2-sensor voltage problems '84 1.9L  -- Help needed lead
              voltages!
Comments: To: David Beierl <dbeierl@ATTGLOBAL.NET>
In-Reply-To:  <4e5512aa.87b9340a.5414.2e70@mx.google.com>
Content-Type: text/plain; charset="US-ASCII"

I tried to provide an extremely simplified explanation of why there is a measurable voltage on the O2 sensor lead for those that do not understand. As for the engine not needing an O2 sensor that is correct. For most all US vehicles 81 and later it is there with a "3 way" catalyst. The 3 way cat also helps to reduce NOx emissions. The O2 sensor keeps the engine from going too lean as excess O2 increases NOx emissions and the 3 way cat needs a perfect mixture in order to work.

Dennis

-----Original Message----- From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of David Beierl Sent: Wednesday, August 24, 2011 11:03 AM To: vanagon@GERRY.VANAGON.COM Subject: Re: O2-sensor voltage problems '84 1.9L -- Help needed lead voltages!

At 11:26 PM 8/23/2011, Dennis Haynes wrote: >circuit. With nothing connected there is a voltage between the lead and >ground most likely the bias voltage or forward drop of the base-emitter >junction. When the O2 sensor is connected before it generates it's >voltage it acts as a load and sinks this voltage to near zero. So yes >you can measure a voltage on the O2 sensor input connection.

Dennis, the resistance of a cold sensor is greater than 40 megohms, so it's not going to load the ECU down any (which is why it stays at half a volt until the sensor gets hot and begins working). If you want me to actually prove it I'll have to trace the circuit, but I'm confident that the voltage on that lead is placed there deliberately by the ECU and it's my belief that it's intended to help the ECU determine when the sensor comes on line effectively, i.e. when its output is strong enough to overpower the bias coming from the ECU.

>So when the O2 sensor is not connected, this leakage or bias voltage is >real close to where the ECU would try to adjust it anyway. As such it >is satisfied and does not make any adjustment. This is why leaving the >sensor disconnected will often allow the engine to run OK.

If the engine is in proper working order it has no need whatever of the oxygen sensor. European vehicles didn't have one - they couldn't, because Europe was still using leaded gas at the time. My '84 was bought in Michigan (but built to California spec), delivered in Germany and spent the first 87,000 miles of its life with no CAT and no O2 sensor. VWOA installed them for me after the Navy shipped the vehicle over here. They made a little mistake, since it had been in Scotland for seven years and according to the paperwork the deal was only good for three years, but I asked and they said yes. Apparently there was a little shouting about that later at VWOA...

The sensor may help a faulty engine run correctly, but if everything on the engine is correct, the only thing that cares about the sensor is the CAT.

Yours, David


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