Date:         Thu, 14 Dec 2000 13:11:46 -0500
Reply-To:     James Creech <jacreech@VISUALLINK.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         James Creech <jacreech@VISUALLINK.COM>
Subject:      O2 sensor voltage test
Content-Type: text/plain; charset="iso-8859-1"

The Bosch FI book outlines a test for adjusting fuel enrichment and
determining if the O2 sensor is faulty, for those not having access to a CO
meter:  Run the engine up to normal operating temp. so the sensor is hot;
disconnect the wiring to the idle stabilizer control valve; disconnect the
single wire (near the coil) which runs to the sensor (leave the double wire
connected which heats the sensor) and connect your voltmeter's pos. probe to
that lead (the female connector which goes to the sensor), and the negative
probe to ground.  Then, while observing voltage readings, adjust the hex
screw on the AFM in both directions to determine the lowest and highest DC
voltage.  Numbers should be range between 100 or 200 mV (equals higher
lambda value, equals leaner) and 1000 mV (lower lambda, thus richer).  You
want to set the adjustment at the midpoint between the low and high value,
which should be roughly around 500 mV - for older sensors it can be a
different value, but still you want the mid-value, which will produce a good
balance between fuel economy and power.

Now, my question for anyone who has done this or otherwise knows (Darrell's
Digitool measures this voltage while the engine is running):  I am getting
values much higher, in the 700-900 mV range, with no variation beyond that
no matter how far I turn the screw in or out.  The Bosch book does not
indicate this is a problem, but they do show a graph with a much larger
range of values.  Do I have a faulty O2 sensor?  Or could I have a leaky
AFM, such that the enrichment screw does not have as much effect as it
should?

Thanks,
Jim Creech
87 Westy GL, 2.1