351W CARBED ENGINE PRO

[tom cloud]

EGO ==>> exhaust gas oxygen sensor.  Unless your car is over, say,
20 years old, it's probably got one.  If you're still using your
computer (engine controller), the EGO's being used by that,
so it may be difficult to use as an indicator.  But if you're
carburetted ... I don't think your controller is doing anything
(if it's still controlling your timing, you may have other problems).

Otherwise, the EGO will be in your exhaust pipe somewhere pretty
close to the exhaust manifold.  If it has more that two wires,
it has an internal heater to bring it up to temperature (only works
when real hot!).  You can read about the EGO in any book on emissions
stuff.  Stoichiometric means all of whatever is put into a chemical
reaction us used up -- no left overs.  So, for gasoline, a ratio
of 14.7 parts air to 1 part fuel is the exact ratio where there
is the least unburnt fuel -- least noxious byproducts.  It is
also where newer 3-stage cats work -- they don't work at all off
stoich.  But, power is made with more fuel than stoich (i.e.
A/F > 14.7:1); and economy is made with less fuel (A/F > 14.7:1).
The EGO's output is a voltage function inversely related to the
amount of oxygen in the exhaust compared to the amount of oxygen
in the outside air around it.  If you're running leaner (more O2)
the voltage is lower.  Richer = higher output voltage.  Stoich
(14.7:1 A:F ratio) is about .45 - .5 volts.  The output is not
linear and steeply changes after leaving stoich, but people use
it all the time to help tune their machines.  It's output is "high
impedance".  That means it produces very little current and any
resistive loading will cause it to produce lower voltages, resulting
in erroneous readings.

So, to use it, you must have a meter with an input impedance greater
than 1 megohm.  Every digital meter I know of has in input Z
(Z is electronics term for impedance) of 10 megohms (some are 11).
Analog meters, unless they have internal amplifiers, are rated in
"ohms per volt".  A Simpson 260 is rated at 20,000 ohms/volt.  To
find out it's input Z, multiply the switch (attenuator) position
by the ohms/volts.  So, on the 10 volt scale, a 20,000 ohm/volt
meter would have in input Z of 20,000 * 10 = 200 thousand ohms.
That means an analog meter won't do.


Steve wrote:
>Tell me more about the projection, if you don't mind..

What do you want to know?

> > I have a DPM (digital panel meter) measuring the output of my EGO.
> > You can get one from Hosfelt Electronics: [800-524-6464 (FAX 
> > 800-524-5414)
> > $14.95, their part number 39-165] or use any digital voltmeter or
> > analog meter with an input impedance of 10 megohms or so.  I 
> > connected
>
>Where is the EGO? built into the car?
>
>The DPM is $14.95, and it connects to your EGO?
>
> > This's probably not it, but the EGO helps set the system up.  Look
> > for about .5 volts for cruise (that's stoichiometric: 14.7:1 A:F
> > ratio).  Up to about .8 or 1 volt for power and maybe down to
> > about .2 or so for deceleration.

[snip]