Date:         Mon, 17 Mar 2003 12:29:30 -0500
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: O2 sensor problems
Comments: To: Mark Keller <kelphoto@SHAW.CA>
Comments: cc: Darrell Boehler <midwesty@MIDWEST.NET>
In-Reply-To:  <3E75FF15.6090000@shaw.ca>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 12:00 PM 3/17/2003, Mark Keller wrote:
>I would like to politely suggest that attempting to correct any problem
>with the running of the engine while leaving the O2 sensor connected is
>flatley incorrect.  Disconnecting the O2 sensor should be the first
>step.  If the engine still runs poor, find the problem.  If the engine
>runs perfect, then and only then correct the the O2 sensor faults,

I quite agree.  The closed-loop mode does its level best to iron out any
deficiencies in the rest of the system based on input from the O2
sensor.  If the sensor is correct this lets you run well even if some other
part of the system is out of spec.  If the sensor is wrong (sensor
problems, wire problems, ECU problems, exhaust leaks) then it will force
the engine to run badly.

>Connect a digital volt meter to the black wire, other lead to the body
>of the sensor and look for voltage as you heat it up. Should reliably
>reach .8 volts and then drop as the flame is remove.

This will demonstrate basic working of the device, but not whether its
response time is correct.  I'll also raise the question of how much load
the sensor should be able to drive reliably (or to say another way, what's
the input impedance of the ECU?  It applies a 500mv bias to the line, but
through what size resistor?).  I'll venture a guess that it should be able
to drive a load of at least a megohm, maybe 100 kilohms or less?  Darrell
probably knows... The DMM impedance of 10 megohms is designed to put as
small a load as practical on the signal, so as not to distort the reading.

david

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