At 03:59 PM 2/11/2002, Jay L Snyder wrote:
>I have one of the Bus Depot catalytic converters that has the  hole for an
>O2 sensor (it comes witha threaded plug).  I have thought of installing a
>second O2 sensor in there for diagnostic purposes.

Should not be necessary -- see below.  Also, unless you install a heated
sensor like the 2.1s have you may find it doesn't run hot enough to give
readings at idle.

>and read the voltage output as you are driving.  I have done this with the
>stock one, but you  get steadier readings with it disconnected from the ECU

The reason being that when the sensor is connected to the ECU, said ECU
actively controls the mixture to run rich-lean-rich-lean-rich.  If the ECU
is doing this, your second lambda sensor ought to be giving the same
fluctuating readings as the first one.   Those fluctuations themselves are
your indication that the system is working properly.  The changes are too
fast for a typical voltmeter to measure accurately, so you'll get readings
all over the map above and below half a volt.  If you put a 'scope on the
sensor (using a x10 probe to get 10 megohm input impedance) you'll see a
rough square wave btw about 0.2 and 0.8 volts as the ECU drives the mixture
rich then lean then rich again.

That being said, a second sensor could be used to discover that the
original sensor is bad...seems an expensive way to  do it.  Most things
that kill the first sensor will likely kill the second one too (lead,
acetic acid etc).

david

>and that kind of defeats the purpose.   Anyone already done this?

--
David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"