[Diy_efi] Standard O2 sensor and tuning

[Garfield Willis]

On Fri, 14 Jun 2002 10:18:13 +0200, ingar <ingar at iotech.no> wrote:

>I have made a dual (both engine sides) O2 meter using standard heated
>sensors. As expected it basically shows just lean/rich condition.
>
>Nut in a discussion at corvette forum people claim that it's perfectly
>possible to use a normal O2 sensor for tuning, getting steady
>readings.
>
>What is correct here?

Ummm, you both are. But you're much more right than he is. :)

There DOES exist for every NB sensor a Volts vrs. AFR curve relating AFR
to the NB output. It's just that it's sooooo damned non-linear a curve
that practically speaking, it's next to impossible to use for measuring
AFR even slightly away from stoich. Add into that mix the fact that the
aforementioned curve is also *extremely* sensitive to temperature, and
you end up with this conclusion:

If the guy on the vette forum can tune with his NB sensor, then he's got
the O2 sensor equivalent of 'troop itch' in music. Ifyaknowadamean.
Seriously, look at any NB sensor curve around the rich area of interest
for us all, and ask youself, looking at the curve, "how much does the
sensor's output vary in going from 11AFR to 13AFR?". The answer you'll
find is "not much at all". Then consider that probly 10X that difference
is the amount the signal will change over the normal range of exhaust
gas temp variations. So trying to determing if you're at 11 or 13 when
the signal difference is down in the noise, not to mention the temp
effects, is going to be hard. It can be done, with carefully
controlled/selected NB sensors (LSM-11 is an example), and tight
temperature control of the sensor thru a well-tuned PID controller on
the heater. The Bosch LA-2 AFR meter, a main-stay of racing for ages,
used LSM-11 sensors with good reputation for being accurate. But they
replaced it with the LA-3, which uses WB sensors similar to the NTKs.

Soooo, just reading a stock NB sensor with a meter or some LEDs? One guy
might pull it off with sensor ESP (be 'one' with the sensor :), but
practically speakin, you're right. Many things are possible that are
also extremely unlikely or difficult to repeat. You could win the lotto,
too. Hell, you *could* conceivably win it twice!

Gar


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