O2 sensor response times- catalyst

[Bernd Felsche]

Garfield Willis writes:

>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".

Thought you might. :-) I didn't put a big disclaimer on there to
save on mail volume. You've already distrivuted the huge caveat. Why
repeat it?

>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.

It's the latest book. The book doesn't provide the numbers, other
than the lambda range and the characteristic curve. The current
values are from the data sheet.

Is the NTK any different to the Bosch wide-range lambda probe?

Both use the pump current to indicate the AFR.
Both use a reference cell against which to balance O2 concentration.

As you say; one should be very careful when playing with these
things. Even a switching lambda probe can be destroyed by shorting
the terminals or by using a low-impedance load...

>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.

Why would you deliverately put in so much excess fuel?
It takes you right off the power curve peak. The only scenario I
thought of beforehand was during cold cranking, so that you can
light the mixture. The O2 sensor probably won't be hot enough to
work from a cold start - unless you've flooded the engine. :-)

>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?

Good advice.

-- 
Real Name: Bernd Felsche
    Email: nospam.bernie at perth.DIALix.com.au
     http://www.perth.dialix.com.au/~bernie - Private HP
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