WB Instruments

[rr]

(see below)

Brian L Massey wrote:

> On Sat, 14 Jul 2001 13:26:58 -0400 rr <RRauscher at nni.com> writes:
> > There are two different fuel cut schemes. One is a decel enleanment
> > that occurs when the throttle is lifted. The other is decel fuel cutoff
>
> > (dfco) that occurs during long decel. At 25:19 the afr spikes rich as
> the
> > throttle is lifted.
> > This is due to the drop in manifold pressure evaporating the fuel
> > that is wetting the interior of the manifold.
>
> Be curious to know how long the ECM takes to decide it qualifies as a
> long decel. I guess I'm using the words fuel-cut too loosely. I've just
> begun to read the 747 hac, so I have some more to learn. All my
> experience has been with carbed engines up until now. Are you saying that
> the first decel was too short to actually kick in dfco, and what I'm
> seeing from 25:19+ to 25:20 is just "de"? Sure looks like the actual dfco
> at 25:22- happens pretty fast after MAP drops, but oddly doesn't seem to
> happen at 25:19+, even though MAP drops fast there too. Is it possible
> that if the TPS isn't completely closed, the ECM doesn't apply dfco? BTW,
> is the "de" portion before dfco partly to prevent exhaust system
> backfires by any chance?

Yes (backfires question). DE is based on closing TPS. The MAP is
involved in how much DE is applied. DFCO is based on a bunch of
items: rpm, map, mph, tps, timers. . . At 25:22 is DE.

>
>
> > Decel enleanment is also
> > taking place. That is the short lean spike at 25:20. I was back on the
> throttle
> > before it could get any leaner.
>
> Got it. Tnx.
>
> > All data except for the WB AFR is from the ECM. The rpm is by 25 rpm
> > per bit.
>
> Oh, I see. I guess that means the 8-bit number for rpm is an unsigned
> 0-511 X 25? I hadn't thought about the data coming from different

It's actually 0-255 for 0 - 6375 rpm. This variable is used for 90%
of the tables lookups and various thresholds. The ECM also keeps
the DRP count in a 16bit variable. This is used for the rev limiter as
it will allow rpm values to 10K or more. It is also used for other items.

BobR.

>
> sources. Tnx.  This is only my second view at a logged run with all the
> interesting parts showing, so its taking a while to get adjusted to all
> the data. Very cool. Thanks much for being patient with all the
> questions. I have an sdsefi, datalogger, and hopefully WB coming (build
> or buy decision pending), so I'm trying to study up before the main wave
> breaks over my head! Tnx.
>
> Brian M.
> ________________________________________________________________

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