O2 sensor response times- catalyst

[Garfield Willis]

On Wed, 29 Mar 100 19:30:16 +0800 (WST), Bernd Felsche
<bernie at perth.dialix.com.au> wrote:

>>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?

I am kinda worried about others thinking those numbers were
authoritative, given the source you quoted, and try them, only to damage
their expensive sensor. Thas all, mate. Someone recently mentioned
getting an NTK sensor directly from NTK. If so, they paid *alot* more
than $100 for it from NTK. Those sensors are also quite different in
pumping current requirements, cal res value, even physical construction,
from the ones NTK makes for Honda. Having them side-by-side is quite
revealing. When someone asks for advice on how to do something, you
wanna be careful you don't recommend something potentially damaging. Not
tryna flame ya, just tryna keep my own frustration levels under control.
I'd love to just blurt out all the stuff we've been thru in getting
working/robust hardware, but I can't cuz it's now business. Sigh.

I would like to mention one other facet of these "caveats". Every mfg.
of equipment that uses these sensors has had to build in a number of
electrical safety-measures and checks, to guard against the sensor being
damaged, either during warm-up, or disconnects, or even circuit failure.
So you can imagine my chagrin to hear people say, "yeah, +25 mils should
do it on the rich side". Argh, it's hard to watch.

>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.

I see; when you said those numbers were derived from the Bosch book, I
read too much into the word "derived". Was it the data sheet of the
Bosch sensor, BTW?

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

Yes, of course. You can expect each of them to vary quite a bit as to
driving requirements, etc. The Denso 4-wire widebands are also
considerably different in their pump current requirements. There are
even two of THESE now to contend with and research; one that Toyota
uses, and one that Honda uses on their HX engines. They have different
Denso part nos, as well as looking physically different, but they're
both Denso 4-wire wideband sensors! Cain't assume they're all the same.

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

Yes, the basics/fundamentals are probly all the same if it's a 5-wire.
Yet, witness the recent discussion that suggested the LSU and NTK
sensors may use different circuitry and have different behavior. The
4-wires are again only slightly different apparently. But that doesn't
mean you can take the numbers for one and use them on the other, eh?
That was my point. If you do, you're gonna damage something spendy.
Ooops, there I go AGAIN! Dang. Forgive me, I grew up in poverty as a
child. :)

>>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.

In aviation engine work, it's referred to as "detonation margin". The
excess fuel is used as a coolant basically. And it appears from the
transient nature in EFI turbo engines, that these short rich excursions
at the points of sudden throttle pos change are more like safety
measures to ensure that there *won't* be any sudden unplanned/unwanted
*lean* excursions to light off the expensive fireworks. After those
short enrichments, the mix settles quickly down to somewhere in the
12sAFR for max power. These transients only last for some fraction of a
second. I trust anyone would at least certainly want to see any
transient *lean* excursions occurring under high boost and fast throt
changes? The only reason the Honda wideband ECU uses open-loop for AFRs
lower than 12 is that it probly doesn't *use*/command higher enrichment,
unless under cold-crank or cold-start; and there as you point out, the
sensor isn't likely lighted off yet (takes about 30-40 secs, pretty fast
but still not fast enough), not to mention the fact that in those
regimes with wall-wetting and fuel condensation, trying to measure the
AFR would be a pretty goofy idea anyway. All the commercial AFR meters
go down into the 10sAFR; it's an area people want to at least get a
glimpse at, even if you're only there for a brief moment.

Peace,
Gar


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