Date: Wed, 8 Sep 2004 14:29:16 -0500
Reply-To: Aerowolf <aerowolf@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Aerowolf <aerowolf@GMAIL.COM>
Subject: Re: Do I need a HEATED O2 sensor?
In-Reply-To: <002101c495ad$903093c0$1302a8c0@comcast.net>
Content-Type: text/plain; charset=US-ASCII
On Wed, 8 Sep 2004 07:10:14 -0700, Tom Young <tomyoung1@comcast.net> wrote:
> From: "Aerowolf" <aerowolf@gmail.com>
> To: "Tom Young" <tomyoung1@comcast.net>
> Cc: <vanagon@gerry.vanagon.com>
> Sent: Wednesday, September 08, 2004 2:21 AM
> Subject: Re: Do I need a HEATED O2 sensor?
>
>
> > If you have a water-cooled catalytic converter [which, by the
> > way, is probably a bad idea anyway for various reasons],
>
> Care to expand on that? Ron at the Bus Depot proposed this combo -
> air-cooled Federal crossover pipe, water-cooled catalytic converter and
> water-cooled muffler - as a way of adding an O2 sensor to the air-cooled
> Vanagon. Off hand I can't see any problem with this combo, though I'll
> admit I don't have an extensive knowledge of catalytic converters
Ah, okay, I was confused (I thought the catalytic converter itself was
cooled by water flow).
The purpose of the O2 sensor is (going to my Bosch book) to help the
ECU gauge whether the mixture is too rich or too lean. This is
gaugable because O2 sensor has a very distinct and extremely detaled
response curve at the "stoichometric ratio" of approximately 14.7
parts oxygen to 1 part fuel.
However, the ECU's operation can't give perfect emissions output
without heating up the catalytic converter, which catalyzes (in high
heat) more of the CO into CO2 and reduces the amount of NOX by
splitting it up into nitrogen and oxygen. When it isn't hot enough,
it doesn't catalyze -- and when the mixture is too rich (due to a bad
O2 sensor) for too long of a time, it actually carbonizes the ceramics
in a way that prevents the catalization from occurring.
Why did you want to put an O2 sensor on it in the first place?
> > then the
> > temperature of the catalytic converter can't get above 100 degrees
> > centigrade -- perhaps a little bit more. The O2 sensor MUST be at
> > least 800 degrees Fahrenheit -- that's 426 degrees centigrade -- to
> > react properly to the presence of oxygen. You're on the right track
> > -- it's not getting hot enough -- but it's very unlikely that it CAN
> > get hot enough even with a heater.)
>
> I thought the heater was supposed to heat the O2 sensor to operating temps
> during the first few minutes after startup when exhaust temps alone weren't
> sufficient to get the O2 sensor operating properly. Since I'm *speculating*
> that my problem is that the O2 sensor isn't hot enough I'd of thought the
> use of a heated sensor would do the trick. No?
The ECU is designed to compensate by running richer in the first 45 to
90 seconds of running, before it gets coherent signals from the O2
sensor.
> > I'd suggest moving the O2 sensor back to where it's supposed to be,
> > and sealing the bung on the cat. Not only will this get the tip back
> > in the flow of exhaust, it'll also put more metal between the O2
> > sensor and the cat, thus giving more material for the heat to have to
> > travel through, and thus letting your O2 sensor get up to and stay at
> > operating temperature.
>
> The O2 sensor *is* back where it's supposed to be. The only problem I can
> see is that the anti-fouling device I'm using in place of an O2 sensor bung
> doesn't get the tip of the sensor as "deep" into the exhaust flow as the
> bung would, thereby not allowing it to get hot enough.
Normally that shouldn't be a problem, since like I said the laws of
thermodynamics will cause it to get hot anyway. But, also like I
said, the exhaust itself needs to flow through the tip so it can
properly chemically react with the platinum wire.
> > (Now. Having said all that: I'm something of a newbie to all of this.
> > I have a bunch of book knowledge, but that doesn't mean I'm right.
> > Anyone got anything to add, or any experience different?)
>
> Only more questions, I'm afraid. Use of the anti-fouling device has been
> reported to work by others; I'm just not sure why it's not working for me.
What's the specific anti-fouling device you're using?
-Kyle Hamilton
