more 747 questions

[Gregory A. Parmer]

On Mon, 8 Jun 1998, steve ravet wrote:
> I'm still confused.  This table lists desired A/F ratios, right?  But at
> WOT you're not measuring A/F because you're ignoring the O2 sensor. 
> Having a table of A/F values seems to imply closed loop operation in
> that you measure A/F, compare to what's in the table, and adjust if
> necessary.

Steve, and others,
  If you haven't ran across it yet, the following URL offers
some super insight. It describes the GN system but I
expect it will apply to all delco systems. The ECM
learns differences required to achieve appropriate A/F
mixtures at part throttle conditions (and sets the Block
Learn Multipliers) and applies the same multiplier
even when you go WOT.  In other words "open loop" is
not entirely based on a pre-programmed map. The BLMs
provide a learned fudge-factor.

See
http://www.thrasher-ep.com/cal_hints.htm

For some almost as good O2 info, see
http://ni.umd.edu/gnttype/www/ecmpage.html

Now for my probably wrong interpretion of the whole
shebang:
What I'm beginning to conclude is that the O2 is 
only of a feedback mechanism to prove that what the 
ECM thinks its doing is really what's happening. For 
example, the ECM enleans and then checks O2 to see 
that it really worked. It richens and checks. If that 
works it can figure (guess?) that it is close to 
stoich and that XX  amount of extra fuel would be required to go 
to 12:1. Open loop just eliminates the check and
gives it the authority to do even more precision 
guesswork.

Gurus..am I just slow, or slow and stupid too? Regardless,
the Thrasher page is worth a read for 101-ers.

-greg