Date: Tue, 26 Jul 2005 16:08:37 -0400
Reply-To: "Bostig Eng." <syncrolist@BOSTIG.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: "Bostig Eng." <syncrolist@BOSTIG.COM>
Subject: Re: Air fuel tuning technique - Gurus wanted
In-Reply-To: <vanagon%2005072615055470@GERRY.VANAGON.COM>
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Hi Dennis,
That's about the best you're going to be able to do with a narrowband...
You're only going to be able to tell three things with the narrowband...
rich, stoich, lean... unless you've calibrated the sensor and can
know/maintain its operating temp. The narrowband slope to either side of
stoich (usually .45v or so) is really really steep, and can vary wildly
depending on sensor temp.. so your observed .7v or .8v could be a AFR of
say 11 if the sensor is hot, or closer to 14 if it's cold.... on top of
THAT you really need to measure in millivolts to even come close to being
useful anyhow I've seen .04 volts equal 3 points AFR on a narrowband. Then
on top of these two concerns you have to make sure your DVM or in this case
gauge, and eyes are fast enough to actually see what's happening. This is
why the narrowband is pretty tough to use for anything other than watching
the crosscounts and average for stoich and knowing that you're rich or lean
but not by how much. It's kind of like testing your fuel level by sticking
an arbitrary length of wire with a piece of cotton on the end into the gas
tank.. if it's wet you've got fuel... but you won't really know how much.
As for the .68-.8v while above 4000 rpm, you can't really know what AFR
you're running in open loop there, just that you've lowered it a bit... it
is still rich but you won't know by how much. I don't think you are going
to blow up your engine as you seem like you're taking your time, and are
being careful, but it IS possible of course. You could be running way too
rich and gas washing the cylinder walls, but if you observed a slight drop
in AFR from a "pegged" .8v to a switching .68-.8 you know you've gone the
right direction (again you don't know by how much though) but in any case
it isn't *worse* than before. I'd really advise you to pick up a wideband
or borrow one and see what is really going on... you'll have a better
running van, and piece of mind. Use the narrowband to watch the crosscounts
for fun, or to tell you if the O2 is on it's way out, but not to tune.
Hope this helps,
Jim
________________________________________
Jim Akiba
Bostig Engineering
http://www.bostig.com/products/zetec/
978.772.3274
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