WB Instruments

[Brian L Massey]

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?

> 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
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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