EGOR - how is he under PRESSURE?

garfield at pilgrimhouse.com garfield at pilgrimhouse.com
Thu Jun 4 00:19:59 GMT 1998


On Tue, 02 Jun 1998 22:31:43 -0700, garfield at pilgrimhouse.com wrote:

>3.6% error from a delta of 1.5psi in exhaust gas pressure

I realized from some private email, that I had failed like the putz I
am, to put in some really important info, namely the "polarity" of this
error, during that last post/report on this issue.

>From both the input Brock had, as well as the NTK plots in the SAE
article, the effect of the error is the following (read carefully lest
you get tangled in it, it's kinda a brain-twister):

The effect of the error is for the sensor to report LEANER mixtures than
are actually present, in the presence of elevated exhaust gas pressure.
This causes the mixture to be set slightly RICHER than intended, by the
engine mgmt. system. So, of the two directions the error could go, this
is by FAR the most desirable, cuz it says that IF you use EGOR in an
engine mgmt. system, let's say with some boost that's effecting his
sanity, he will report that the mixture is leaner than it is, and so the
result will be you will run a tad richer than you intended. That's
CERTAINLY far better for our "racing/aircraft/performance/survival"
focus, than those to whom minimum emissions is the grail they seek.

See why I said it was unfortunate to omit this info? Cuz if the
direction of the error had been in the opposite direction, we'd REALLY
be in a world of hurt, cuz that would mean EGOR's pressure-induced
derangement could be responsible for your engine running too LEAN. A
thing he should wanna do NEVER. This way, his error is gonna cause your
ECM to err on the side of too rich, rather than the potentially fatal
side of too lean. Phew, thank God for that!! And the percentage RICH you
would be running would presumably (assuming the fuel maps are linear,
har har) be this same 3.6% per 0.1atm pressure delta effect. So, if
these errors ARE indeed what we'll see from the Honda NTK sensors (a
fact I STILL have some doubts about, in light of the commercial box
mfg'ers saying nuthin bout this), then if you had a 1.5 psi backpressure
(which hopefully is 0.1atm roughly B), your mixture would actually be
3.6% lower (richer) in AFR than EGOR measures, assuming you do NO
compensation.

Hope that helps take the chill and edge off that earlier cautioner's
tale. At least, IF this effect is there and as strong as the SAE paper
indicated, then we err on the "good side".

Gar




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