Correct A:F Ratio @ WOT?

[Bernd Felsche]

Jon Davis tapped away at the keyboard with:

> I don't want to measure the output of the O2... I can do that with
> my DMM. I am going to make a circuit that adds an offset to the
> output of the sensor to tell some lies to the ECU. I wanted to
> know the esr so I could make the output of my offset circuit mimic
> the sensor better. Guess I'll just shoot for 100k and call it good
> enough. When I measured the output of my O2 during closed loop
> cruise, the average was .56 V which seems a little rich.

You can raise/lower the _voltage_ level using an op-amp to "add" the
required offset voltage. This can be done without knowing the
impedance of the sensor (as you'd typically have a very high input
impedance on the op-amp). It's fairly simplistic, but should work OK
for your requirements.


> ----- Original Message -----
> From: "Bernd Felsche" <bernie at innovative.iinet.net.au>
> Sent: Tuesday, October 02, 2001 4:50 AM

> > Jon Davis tapped away at the keyboard with:
> > > I have wondered about real vs. indicated AFR... some mods on my
> > > car seem to do real well for about a week, but the power slowly
> > > disappears over time. I wondered if I was changing the combustion
> > > and screwing up the self-learn in my ECU. I thought about making a
> > > circuit with a variable offset on the O2 sensor, to tell some fibs
> > > to the ECU and see what happens. Anyone know the esr of an oxygen
> > > sensor offhand, around 100k?
> >
> > It may be "broken" if you try to run a resistance measuring current
> > of any magnitude through it for any length of time.
> >
> > One measures the output voltage into a high impedance (>1Mohm).
> > The ECU is probably looking for the switching voltage about 0.45
> > volts, which is equivalent to stoich.

-- 
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