O2 Sensor Bias

[Chris Conlon]

------ =_NextPart_000_01BDD158.44E30DA0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit

Larry wrote:

> A lot of guys play with fuel pressure to alter their WOT O2 readings. I
> understand that GM runs the stock motors a bit rich, and a lot of guys
> lean them out to get more power.
> ...
> shouldn't it be possible to just place a resistor inline with the O2
> sensor to "trick" the PCM that the O2 sensor is reading a higher voltage
> than it really is, and thereby lean the mixture accordingly? Maybe I'm
> barking up the wrong tree here...but is this possible? How? Any
> problems?

I don't know if any of this will help lean out WOT operation, but the
question about the resistor got me scratching my head some.

You probably could use a resistor tied to a 1v bias to make the sensor
read a wee bit higher. (I'm pretty sure I've even seen flaky-looking
commercial products designed to do just this.) Picking the resistance
would probably be a pain. Also does an O2 sensor's output impedance
vary much, within the warmed-up temp range? This mod would probably
also mess up the 0.450v bias used to tell if the sensor is warmed up
or not, maybe leading to problems during warm up?

The clever way requires you to have faith that the O2 sensor reading
is meaningful (not necessarily linear but repeatable) away from stoich.
Ok this isn't really true of an O2 sensor, but just pretend for a minute.
What you want, roughly, is an O2 sensor who's output crosses through the
450mv range at say 16:1 rather than 14.7:1. Suppose your O2 sensor
reads 380mv at 16:1 (wild guess). Essentially you generate a 380mv
reference, and take the O2 sensor signal, and feed the 2 into a
comparator, or even an op-amp set up for maybe 20:1 gain. Divide and
buffer the output as needed for a 0-1v range, and feed that into the
ECM's input. Congrats, your ECM will now see cross counts at 16:1
instead of 14.7:1, and adjust the AF accordingly. (If it doesn't freak
out anyway.)

Problems:
This also defeats the sensor-warmup detection via the 450mv bias.
You could add some more circuitry to get around that.

The sensor voltage corresponding to 16:1 probably varies a good bit
with operating conditions, and the curve is steep to begin with. If
you had a wide-range O2 unit, well, that would be nice. :)

How lean do you want to run? Detonation could be a real problem
depending on the engine.

I realize this isn't a very useful solution to Larry's original
problem... but once the question of tricking the O2 sensor got
into my head I just had to think about it until I was satisfied.
Hopefully someone will find it useful or interesting.

   Chris C.

------ =_NextPart_000_01BDD158.44E30DA0
Content-Type: application/ms-tnef
Content-Transfer-Encoding: base64
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------ =_NextPart_000_01BDD158.44E30DA0--