Date:         Tue, 23 Aug 2011 10:02:31 -0700
Reply-To:     jhlauterbach <jhlauterbach@BELLSOUTH.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         jhlauterbach <jhlauterbach@BELLSOUTH.NET>
Subject:      Re: O2-sensor voltage problems '84 1.9L  -- Help needed
Comments: To: David Beierl <dbeierl@attglobal.net>
Content-Type: text/plain; charset=us-ascii

Hello David:


I fired up the 1968 model Heathkit VTVM and checked it out with various
batteries.  Voltage from O2-sensor is zero, even after engine warms up.

Time to order another O2-sensor and see if it will last longer than this one
did.

Thank you for your help.

John




________________________________
From: David Beierl <dbeierl@attglobal.net>
To: John Lauterbach <jhlauterbach@BELLSOUTH.NET>
Cc: vanagon@GERRY.VANAGON.COM
Sent: Tue, August 23, 2011 10:09:14 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