[Gmecm] BLM cell confusion

[Steve Ravet]

> -----Original Message-----
> From: gmecm-bounces at diy-efi.org 
> [mailto:gmecm-bounces at diy-efi.org] On Behalf Of Ryan Hess
> Sent: Sunday, October 30, 2005 12:37 PM
> To: gmecm at diy-efi.org
> Subject: [Gmecm] BLM cell confusion
> 
> Hi everyone,
> 
> I'm working with the $A1 code, and have been slowly
> conquering a steep learning curve.  I'm still greatly
> confused about the BLM cells.  How they work, and the
> differences between cell 0, 1 and 2...  For instance,
> I've gathered cell 0 appears to be closed throttle
> idle conditions.  The others I don't know.  Secondly,
> how do the BLM cells increment?  They follow the INT,
> but how?  'preciate it,
> 
> 

The INT is part of the feedback loop and so constantly moves up and down
as the ECM maintains stoich.  There is no "history" with INT, it just
changes to whatever value is required.  The BLM provides the history.
If the INT is consistently high or low for a period of time then the BLM
will start to move in that direction.  Both INT and BLM are part of the
fueling equation, so as BLM starts to move INT will tend back to
neutral, or 128.

So say you had a plugged cat.  The reduced airflow will cause the INT to
drop and cut back on fuel.  Since the INT is consistently below 128 then
BLM starts to drop also.  As the BLM drops and cuts out fuel, it allows
INT to rise back around neutral.  So right after it plugs you'll see
normal BLMs but low INTs.  As time goes by (maybe a few minutes?) you'll
see BLM drop and INT rise back to neutral.  Then the opposite happens
when the cat is fixed, and eventually both of them rise back to near
neutral.

Generally BLM is a table indexed by MAP and RPM, like the VE table.  I
think there are exceptions where there is one BLM number for idle and
another for everything else.  Not sure about your specific situation.

--steve