Re: [Tech]Why measure CO? re:ignition timing and res

[Brad Sheridan <brads@mindspring.com>]

At 04:59 PM 5/25/01 -0400, you wrote:
>So the Bentley and many of you have mentioned measuring CO to set the
>mixture, and i'm sure that was the way it was done on this car originally,
>but why not use the O2 sensor?  We all have that sensor, whereas we have to
>find some way or buy some gadjet to measure CO.  The thing should be
>disconnected during adjustments anyway, shouldn't it?    It's supposed to be
>a final correction to the mixture, so the mixture should be tuned to give
>the best "average" result without the sensor [IMHO].  Why not just hook up a
>voltmeter to it and tune away?  That's essentially how we do the first few
>rounds of tuning on the Formula project I work on, so why should we use
>anything different for a Scirocco?

>Actually we don't use a voltmeter, but instead we have a custom built meter
>that uses a running bar graph to show the mixture, but a good DVM, or even
>analog, will do the same.  There was a website somewhere that showed how to
>build one of these Lambda meters for a few bucks.  Of course I can't find
>the link at the moment, but ask me if you want it.

  A cheap one can be built with an LM3914 bar graph display driver for a
few bucks. But you get what you pay for. Actually you get less, because you
are using an O2 sensor to tune in a range its not designed for, but thats a
completely seperate issue. If you want a reasonably priced O2 sensor
display try http://www.jumptronix.com They make one with a numeric display
of voltage (more precise than a few leds), for $85. 

  And as for your formula project, I would really consider looking into
using a 4 gas analyzer to set up the fueling, it gives you a much better
idea whats going on, and can help you tune for cylinder to cylinder
variations where a typical O2 sensor cant do that as well.

Brad




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