thanks for making sense of this David.

----- Original Message -----
From: "David Beierl" <dbeierl@ATTGLOBAL.NET>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Tuesday, August 23, 2011 7:09 AM
Subject: Re: O2-sensor voltage problems '84 1.9L -- Help needed

> At 09:31 AM 8/23/2011, John Lauterbach wrote:
>>Here are the details.  O2-sensor not connected.  Voltage from O2-cable
>>coming from engine is +0.46 volts.  Again, O2-sensor is not connected.
>>I have tried with two different ECUs and get same result.
>
> This is normal.  The ECU applies a bias voltage to the line so it can
> tell when the sensor heats up and comes on line (and swamps the bias
> signal).
>
>
>>With engine off, resistance between O2-cable coming from engine and
>>ground is 140K ohms.  I have a spare FI cable assembly and get same
>>resistance from that cable when a ECU is connected.
>
> That sounds like a not-unreasonable value.
>
>
>>If I connect O2-sensor as intended, engine runs rich and stalls.
>
> Using a digital meter,* describe the behavior of the O2 sensor while
> disconnected from the ECU and engine running, blipping throttle, fast
> idle and such.
> I'm expecting that you're going to see output of zero or close to it
> under all running conditions.
>
> Connect the sensor (ok to do while engine running) - I expect you'll
> still see zero or very low output.   This would indicate either bad
> sensor or oxygen getting into the exhaust through misfiring cylinder
> or exhaust leak.
>
> *Oscilloscope would be great, analog meter would also be great but
> would need sensitivity of  at least 40-50 kohms per volt and set on
> maybe three-volt scale.  An indicator based on an LM3914, such as the
> one that Ken Lewis sells would also be excellent.  Since you probably
> don't have any of these, a regular digital meter on two-volt scale is
> usable though unwieldy.  If it has a fast-acting bar-graph as part of
> the display that would help.
>
> Yours,
> David