O2 sensor response times- catalyst

[Garfield Willis]

On Wed, 29 Mar 100 10:22:49 +0800 (WST), Bernd Felsche
<bernie at perth.dialix.com.au> wrote:

>Will McGonegal writes:
>
>>Just for anyone interested, in the NTK wide ratio sensor manual it
>>states that the O2 "pump" current varies from -12.5 to 12.5 mA, the O2
>>sensor is biased with a 25 uA +/- 3 uA current (the sensor output
>>voltage (450 mV for stoich) is read on top of that).  The heater
>>voltage is 10.5  +/- 0.5 volts.  I still don't know how you go from
>>pump current to AFR!
>
>This is derived from the new Bosch SI Engine Management book:
>
>The -25 mA would correspond to approx lambda of 0.7, +25 mA to
>approx 2.2. 0 mA is lambda = 1.
>
>You should be able to fit a curve through those three points.
>
>Not that it's not often useful to have a lambda of 0.7 - that's way
>more rich than any steady-state running would require.

Argh. All I'm at liberty to say to the immediately above is "BZZZT".
Remember I warned ya, these devices are both spendy and VERY easy to
destroy by over-pumping or mis-pumping (pumping in the wrong direction).
It's referred to in the trade as "blackening" the sensor. Others who
have worked with these sensors in industry and have no commercial
interest in them as I do, will also confirm this. I shit you not.
Besides, I'm surprised that a Bosch book would even mention an NTK
sensor, but those numbers aren't even close.

BTW, 0.7 lambda is roughly 10AFR. WOT turbo engines can/will fuel in the
10'sAFR during transient enrichment under heavy load, so altho this
isn't "steady-state running", being able to see and measure these rich
excursions isn't so far afield. And carb'd engines will lean-misfire and
even backfire, if idle-jetting combined with a rapid undamped
throttle-off runs the AFR to above 17-18, so measuring to this lean,
again altho not "steady-state" still can be important, too.

I won't be saying too much more about tech stuff concerning these
sensors; as an instrument vendor I'm just not able to participate the
way I'd like to, without raising suspicions of bias. C'est le vie. Just
caveat your emptors, doods, and save at least one good, pristine,
virgin, unmangled sensor for EGOR, will ya?

TTFN,
Gar


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