Date: Wed, 8 Sep 2004 04:21:06 -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: <004301c49549$95ddaa60$1302a8c0@comcast.net>
Content-Type: text/plain; charset=US-ASCII
The O2 sensor must be at exhaust temperature to function properly --
if it is too cold, it will read high resistance values, which
indicates to the computer that it needs to richen the mixture.
As well, the tip MUST be in the flow of exhaust in order to get the
proper O2 reading -- it's a very thin platinum wire that responds to
the presence of oxygen in the exhaust.
There are very good reasons why, on the stock Vanagon, it's located
before the catalytic converter, in the flow of exhaust. (Remember the
laws of thermodynamics -- heat will move from hotter areas to colder
areas. If you have a water-cooled catalytic converter [which, by the
way, is probably a bad idea anyway for various reasons], 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'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.
(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?)
-Kyle Hamilton
On Tue, 7 Sep 2004 19:14:33 -0700, Tom Young <tomyoung1@comcast.net> wrote:
> Hi all:
>
> For many years I've been using the O2 sensor in my California Vanagon to
> adjust the basic air/fuel mixture; that technique has worked fine.
>
> When I rebuilt my Federal Westfalia (no O2 sensor) I installed a
> water-cooled catalytic converter in the exhaust. Since the water-cooled
> converter has the O2 sensor bung I figured I could install an O2 sensor here
> to adjust air/fuel mix.
>
> The first time I tried it I was getting readings so low (indicating "too
> lean") that I couldn't believe it; the van was running well and screwing the
> adjustment screw all the way in basically had no effect on the readings.
> Since I was using an new O2 sensor the only thing I could think of was that
> the O2 sensor wasn't getting hot enough as the catalytic converter has a
> much larger diameter than the crossover pipe, thereby cooling the mixture.
>
> Accordingly, I installed an 18mm spark plug "anti-fouling" device in the
> exhaust in the crossover pipe. The only thing is, since the anti-fouling
> device is quite a bit longer than a standard O2 sensor bung (couldn't seem
> to find one locally) the O2 sensor's tip is not fully in the crossover pipe.
>
> Again, the readings I was getting from the O2 sensor (new sensor, remember)
> were extremely low. Since I just failed my Smog today (too-high HC,
> too-high CO) I know these readings aren't correct. Again, I'm *guessing*
> that the problem is that the O2 sensor isn't getting hot enough, since the
> tip is not fully in the flow of the exhaust.
>
> So, I'm thinking I should buy and install a *heated* O2 sensor; if my
> problem is that the single-wire sensor isn't getting hot enough, that should
> work, right?
>
> Or am I missing something else here?
>
> TIA.
> ---------------------------------------------------------------
> Tom Young '81 Vanagon
> Lafayette, CA 94549 '82 Westfalia
> ---------------------------------------------------------------
>
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