EGO

[Clare Snyder]

----- Original Message -----
From: DIY_EFI Digest <DIY_EFI-Digest-Owner at efi332.eng.ohio-state.edu>
To: <DIY_EFI-Digest at efi332.eng.ohio-state.edu>
Sent: Wednesday, December 15, 1999 5:00 AM
Subject: DIY_EFI Digest V4 #696


> Date: Tue, 14 Dec 1999 14:16:01 -0800
> From: "John Dammeyer" <johnd at autoartisans.com>
> Subject: re: Pulse Wdith.
>
> >John Dammeyer <johnd at autoartisans.com> wrote:
> >
> >>If it's a standard O2 sensor why not replace it with a pot that provides
> >>0..1.0V and set the output to 0.5V which is supposed to be 14:7:1.
Then,
> >>because the O2 is telling the ECU that the mixture is perfect it won't
keep
> >>screwing around with the mixture pulse width and you can see the real
result
> >>of your tuning.
> >
> >I have little experiance in these things, but don't OEM controllers
richen the
> >mixture until they see the O2 sensor make a "transition" from low to
high, and
> >then they lean the mixture until the voltage goes back down.
> >
Correct - Strandard computers, with standard O2 sensors count the
transitions to  monitor sensor. No transitions means bad sensor - goto
backup mode (open loop)

> >Holding the O2 sensor voltage constant would have an unpredictable
effect.
> >Possibly the computer would flag it as faulty and use some sort of backup
> >system.
>
>
> I don't believe that's true.
Trust me, it is.

> The HEGO sensors have a voltage output of 0.5V at
> 14.7:1 and then the voltage changes rapidly on either end and so the
sensor
> appears to have a on/off value.

Not only appears to have - the computer does not read absolute, but adjusts
the mixture lean when it gets too rich, and rich when it gets too lean. By
doing this very quickly it holds an average steady state.

> Perhaps some engine controllers do just use a
> simple go/nogo approach but I doubt it.  I can adjust the mixture so the
O2 puts
> out 0.55V or 0.6V etc.

You can, but the computer can't.
The wide range ion-pump type units work differently, as they are linear in
output. A given voltage means a given A/F mixture (close enough for our
purposes - not technically 100%true, so forget the flaming)
 >I have no clue if 0.55V is 14.1:1 or 10.1:1

Nor does the standard O2 sensor

> but I do
> know that with a properly set up engine with an Ellison Throttle carb. or
else
> an SU carb that at maximum Torque the O2 sensor is at about 0.75V.  I've
set my
> fuel injection to be roughly the same.  Exhaust Gas Temperature and a Post
Run
> check of the spark plug colour all confirm the mixture is 'about' right.
>
> Cheers,
>
> John
>
> ------------------------------