Re: EPROM Programming

[rr <RRauscher@nni.com>]

You have to watch out when changing the blm boundries. The
'747 in particular will stop learning once outside of the blm cell
rpm/map bounds, but will continue to do fuel corrections based
on those cells, when outside of the boundries.

(I'm having trouble thinking how to explain this. . .)

Say the max rpm boundry is 2000 rpm, the ecm will continue
to do a blm learn as long as the engine speed is below that 2Krpm.

Once the engine speed is above that 2K, learn is turned off.
However, the ecm will continue to use those cells that stop at
2Krpm, to change the fueling. The ecm just picks whichever
one covers the current map value.

This is also true for the map boundries.

I discovered this quite accidentally when I attempted to cover a
small area of the ve table with the blm cells. Darn near couldn't
drive the car once those cells started changing.

(a reason I always carry an eprom that I know works <g>)

BobR.

Scot Sealander wrote:

> David Posea wrote:
>
> > Ok, it's question time here. Does the GM adaptive control function at all
> > times, or only in closed-loop trying to maintain 14.7:1 A/F?
>
> There are really two parts to this question.  What does it do in
> closed loop and open loop.  The feedback part that actually changes
> the BLM is only active when the AFR is at stoich. This is because the
> feedback device (the O2 sensor) only functions properly at that AFR.
> This mode is closed loop.
>
> When at WOT, the ECM goes open loop and is no longer at stoich AFR.
> It is in open loop, even if the scan tool still says it is in closed
> loop.  Once on, GM usually never shuts off the closed loop flag unless
> the O2 sensor dies.
>
> Now does the ECM use what it has learned from O2 feedback at WOT, or
> open loop mode?  Yes. They all add fuel if learning has told it to
> add fuel.  Most, but not all, will not let the code remove fuel if
> in PE, and it has learned to remove fuel.
>
> You can change BLM boundaries so that the ECM will not learn in
> the BLM cell used at WOT.  So then, when in WOT, the fuel will not
> be altered from the normally calculated value.
>
> Good advice is to know your cal...
>
> Scot Sealander
> ----------------------------------------------------------------------------

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