There is a way to test the O2 sensor system for response. With the engnine warm and running, short the O2 sensor lead to ground. The engine should go rich. You can use the voltmeter to confirm this as the O2 sensor voltage should go up. You want to see ~.8 to 1.0 volt or more. Now connect the sensor lead to voltage source/ This should drive the ECU to make the mixture lean and this will make the O2 sensor voltage drop. 

As the ultimate test reconnect the O2 sensor. Measure the voltage on it and see if it is fluctuating. If it is then it it is working and your perceived richness may actually be something else such as an ignition or lean cylinder miss fire or maybe something more cylinder such as valve problem. 

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of John Lauterbach
Sent: Saturday, August 13, 2011 11:47 AM
To: vanagon@GERRY.VANAGON.COM
Subject: O2-sensor blues and more on '84 1.9L engine

First, thank you to one of the list gurus who suggested checking on shorts between O2-cable and its shield.  I had one of my own causing.

When the O2-sensor is connected and I measure the voltage between the connector and engine ignition control module heat shield, I am getting around 0.46 volts with engine warmed up.  Voltage is rather stable with engine at idle.  Am I in the ballpark?

With O2-cable unplugged, resistance between connector and ground on cable to O2-sensor is infinite.  Resistance between other connector and ground on cable to ECM is 173000 ohms.

I am not sure what I am missing, but engine runs well, but is running very rich.

John