another angle - using a NTK (honda) sensor with a speedpro

[Garfield Willis]

On Wed, 20 Sep 2000 00:19:32 -0700, Carl Summers <InTech at writeme.com>
wrote:

>    Obviously we can't all span gas test our wbo2's daily...all I can tell
>you from experience is if the mixture is fuel rich, the sensor doesn't last
>as long.  I have seen over 100 hours on a wbo2 on leaded fuel, but AFR was
>never below 12.2:1....btw Powertrain.net has a shield available to cover the
>inlet side of the sensor so it won't foul as easy.....hth's

Good input Carl, I've also seen the caution in several places, about
"the richer you run, the shorter the life". But as you say, you're
probly not burdening the sensor too badly in the 12sAFR; it's just if
you were running for long periods in the 10sAFR say that you're probly
hurting it some. Our XA experience with leaded AV gas and O2 sensors
in general also suggests that the shielding does help some too.

But it won't usually be necessary or even longed-for (precision gases
are spendy; ask me how I know :), the ability to span-gas (sample
gases of known equivalent AFR) test, AS LONG AS the instrument has a
free-air calibration procedure. This is another thing that's sadly not
done on the SpeedPro's. They likely could have included it, but that
would presumably have obviated their "proprietary sensor" scheme
(obviously if you can free-air re-calibrate the intial sensor, you can
swap in a new one and re-cal it). Consequently, on the SpeedPro, I'm
not sure if there's any way to judge how much you've degraded from the
original calibration, as time goes on. Probly not. Argh.

With EGOR and some of the other AFR instruments that have free-air
calibration, like the Horiba's, you CAN see the degradation from
contamination, because the early effect of the contamination is
"occlusion", where the pores of the sensor begin to clog from the
deposition of contaminants, and this tends to shift the entire sensor
curve toward a weaker output level overall, and this you would notice
by your calibration settings "trending" in one direction over time,
each time you free-air calibrated. Once you run out of calibration
room on the free-air adjustment trim, your sensor's officially
departed the living.

The "slow sensor" phenom isn't as easy to see coming on, but I
understand it also doesn't appear until late in life. So the bottom
line is, if you're running leaded with EGOR (or others with free-air
cal), you WILL be able to get some idea of how much it's affecting
your sensor over time, and also when it's about ready to give up the
ghost. Indeed, some of the highend equipment that E.C.M. makes
(>$10K), actually logs the cal trim that's added each time the sensor
is free-air recal'd, and actually gives you an estimate in hours of
how old your sensor is!, based on how far the sensor has moved from
it's cal trim when it was new. Kewl, eh?

Gar


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