Date: Fri, 19 Nov 1999 14:47:07 -0500
Reply-To: Bob Donalds <bostneng@FCL-US.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Bob Donalds <bostneng@FCL-US.NET>
Organization: Boston Engine Exchange
Subject: Re: Oxygen sensor questions...
Content-Type: text/plain; charset=us-ascii
Roger Bowman wrote:
>
> Greetings:
>
> I am tracking down a warm start/drivability problem on an '89 syncro westie.
> After the first start of the day, each following start will light off like
> normal, and then settle into an uneasy idle, around 500-600 rpm indicated
> (as opposed to 1100-1200 indicated normally), with no power. There is no
> power to accelerate, and the motor will not rev even with wide open
> throttle. The motor will usually stall, but if it does not, after 10-30
> seconds of poor idle/no power, the motor will surge into normal idle and
> power.
>
> Without fail, turning the motor off and restarting (either by compression or
> starter) corrects the problem immeaditely. I am suspecting Oxygen sensor...
>
> Recent work: New Temp II sensor, new fuel filter. Digifant box replaced
> with rebuilt Bosch unit.
>
> Diagnostic Info: Using my new Fluke 87...
>
> Looking at the Oxygen Sensor: Engine fully warmed.
>
> - Connected to Harness/Digifant:
> I can see the crossovers; voltage ranges from zero/little negative
> (-.05v-0.0v) to over .9 volts, but the voltage seems to spend most of its
> time in the lower range. I frequently was able to see the digits resolve in
> the lower range (around 0.0v), with a crossover about once every 1.5
> seconds. The sensor spent a very short time at the higher voltage, and then
> returned to the lower voltage. This was pretty consistent; lotsa time at
> low/zero volts, short spike to higher voltage, quick return to lower
> voltage. Average voltage indicated by meter: .3v or so.
>
> - Disconnected from Harness/Digifant:
> Digifant side: about .38 volts
> Sensor side: camped out at close to zero. Poor running; replicates
> original problem
> - Pulling the idle stab hose caused the o2 sensor output to soar to
> 0.9V and idle to smooth.
> - Pulling the vac hose from the FI pressure regulator and plugging it
> did not show any change.
>
> So: I'm thinking sensor...and my thoughts cost about $150 or so.
>
> So I pull the sensor and do the bench test thing; find about 3.5 ohms across
> the heating element connection, and when heated with a propane torch, the
> voltage output climbs from 0.0V to 0.9 volts, and falls quickly (within a
> second) when the flame is removed.
>
> Sure would like to confirm a bad sensor before spending all that money; but
> frankly, I'm still not sure it is the Oxygen sensor at all. I expected more
> crossovers then just one every 1.5 seconds, and I would have expected the
> average value to be close to "Stoich" - which I thought was .45v from the
> sensor.
>
> Any help is appreciated...in advance.
>
> Roger Bowman - bowmanrp@ earthlink.net
> Live Smart. Think for Yourself. Transform the Future
Roger
the oxy sensor does not kick in if the throttle switch is not working
properly
Bob
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