Really accurate, I would agree with, but an O2 sensor can only check a/f
ratio right around it's operating range. The computer uses the O2 sensor to
keep the engine running a bit lean (by toggling between being on the rich
and lean side of the curve) But the sensors produce very low voltage
differentials at anything other than their operating point, making it very
difficult to get accurate readings of anything other than the ideal a/f
ratio (there is some data, but it is very hard to calibrate against, and
signal noise usually swamps it out). Take a look at the blue SAE manual,
under (I think) the Bosch O2 sensor if you want to see what the curve looks
like (I can approximate that it looks like the follwong (i.e. almost
completely binary)):
^
1.5V|________
| \
| \
| |
| |
| |
| \
| \__________
0V +---------------------->
<-lean-->^<-rich---->
|
--operating point (somewhere near stoichiometric efficiency)
(I may have the voltage range wrong, it has been a while since I've used
these things)
I know they've done some work to make this look more like an S-curve, so
that closed loop analysis can be more useful, but I remember reading that it
didn't help too much, and the new sensors were really expensive (like
$500?). I couldn't find any data on it though.
.Geoff
-----Original Message-----
From: Tim Berry [mailto:coolva1@home.com]
Sent: Friday, August 18, 2000 8:18 AM
To: dakota-truck@buffnet.net
Subject: DML: Re: Re: Supercharger Guru's (or anyone else thats a guru
with tuning an engine)
I'm running the Autometer A/F meter, which I hooked up to the computer wire
that reads the O2 voltage... so its using an o2 sensor (the stock one)
which means it *should* be really accurate
I got the meter from Summit (part # ATM-3375) which was $49.95
___________________
Tim Berry
Chesapeake, VA
97 CC, 4x2, auto, 318
Best 1/4: 14.10@96.8
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