Proper Mixture.

[tom cloud]

>John:
>
>Here is a web page that will probably answer some of your questions about
>the O2 sensor: 
>
>http://ram.chem.tulane.edu:8080/f-body/trivia/o2sensor.html
>
> From what I've been able to gather, the O2 sensor found on modern cars is
>really only good for a narrow band of A/F ratios,  so narrow in fact that it
>is really only able to tell you if you are over or under the optimum.  Again
>from what I've gathered, this is used to adjust the injector pulse width
>slightly until the mix is a little too far the other way.  So, the A/F mix
>hovers close to stoich but never really stays on stoich too long.  
>
>Nother thing.  The O2 sensor is some distance from the injector and what is
>going on between the two places may bear no relation to either of them.  In
>other words, the O2 sensor tells you what already happened some time ago and
>the system is left to make some sense of it in real time.
>
>BTW, what injectors are you using for a motor that small and what kinds of
>rail pressures are you using?
>
>Best regards,
>Thomas Sparks
>
>
A simple and effective indicator for O2 sensor is a DPM (digital
panel meter) from Hosfelt Electronics.  It is $14.95, their part
number 39-165 (the part no. on the data says PM-128).  It uses an
Intersil ICL7106 DMM chip with a fairly standard wiring.  There is
one problem -- they have connected the supply voltage common with
the input common, which can cause ground loop problems  -- I solve
this by using a 9 volt battery (actually I was lazy and that was
just the fastest way for me to get it up and running).  The 9
volt battery lasts about 6 months.  One could use a simple resistor
and zener or LM-317 to run it off the 12 - 14 volt battery system
(I don't think it wise to run it straight off the auto's battery
system).

It is 3-1/2 digits and can be wired to read 0-2 volts (the lit.
is poor, so if anyone has a problem, I can tell you how to wire
it for this range).  The O2 sensor output is 0 to about 1 volt,
with about .5 volt being stoichiometric (14.7:1 A/F) and more
fuel (lower A/F, higher F/A) producing more voltage.  The sensor
output is Hi-Z and the DPM is rated > 100 M ohm input Z, so it's
ideal for this app.

On my '82 Bronco with the sensor in standard location (about 6
or 8" downline from the manifold), the sensor gets warm enough
to give a reading in a minute or so and allows me to have some
semblance of control and repeatability over my Holley TBI system.

Hosfelt Electronics: 800-524-6464 (FAX 800-524-5414)
$14.95, their part number 39-165.

Tom Cloud