OEM algorithms (DSM)

[Todd Day]

I'm dumping the ROM of the DSM triplets (Talon/Eclipse/Laser).
I found a couple of interesting things and I thought I'd put
'em out there for some comment.

1) The ECU goes through all these fancy calculations for figuring
	out how much fuel it should be pumping out based on the MAF,
	barometer, and air temp.  It then takes into account the
	oxygen sensor for final trim.  At the very end, it intentionally
	enriches the mixture by 1.5%.  I think it does this so that
	it can stay a bit rich on the A/F ratio for emmisions.  That
	sound right?

2) In another part of the code, the ECU is trying to decide whether
	or not to even run oxy feedback at all.  It takes a look
	at the amount of air and compares it against two tables that
	are indexed by RPM.  It ends up with three bands of air flow
	vs. RPM (split by the two tables).  In the low air band, it
	will run oxy feedback.  In the mid air band, it will run
	oxy feedback for 20 secs before going open loop.  In the high
	air band, it won't run oxy feedback at all.  Now, I can under-
	stand what the ECU is trying to accomplish at low and high
	air amounts.  But I can't see what it is trying to avoid in
	the mid air band.  I was thinking it might be due to oxy
	sensor overheating or something, but my friend tells me
	they actually enjoy operating at high exhaust temps.

3) To add to both 1&2, the ECU will not do the 1.5% fattening in
	the mid or high bands.  Any idea why?

Thanks for your comments.

-todd-

P.S.  After wading through 12k of OEM code for a few months (and this was
	code written in the late 80's on an 8bit micro), I just don't
	see how a handful of people in their spare time could even
	come close to the complex cases handled by a manufacturer
	with years of experience.  I've also dumped an ECU (4k ROM) from
	the early 80's that was much much simpler, and I don't even think
	I'd ever think of every case covered by that simpler ECU.
-- 
Todd Day
todd at di.com