O2 Sensor Tweaking...and MAF Enlarging...

[Roger Heflin]

On Wed, 24 Mar 1999, Richard Wakeling wrote:

> Hi Larry,
> 
> 	One of the many maps or tables used by the PCM is called the Air/fuel
> ratio table. Diacom sees this as the commanded air/fuel ratio.
> When set to 14.7 A/F (stociometric) BLM comes into play but when set to
> 12.5 A/F for heavy or full power condition BLM calculations are ignored
> and BLM will be seen as 128 meaning that we are not in closed loop and
> we are sitting some where on our A/F table which is not 14.7. During
> this condition no additional fuel is added by the BLM and this means
> that we can adjust our full power A/F and no that it will not be leaned
> off as you thought it might.
> 
> Cheers Richard.  (Love thoes Delco's)
> > 

They won't learn anymore in open loop but some of the computer do use
the BLM's.  I found the code in mine that detects WOT, and if the BLM
is less than 128 it sets it to 128, above 128 it leaves it.  The
strategy seems to be leave the engine as rich as seems correct, and
don't dare go lean.

So some of the adjust will be taken out by the BLMS.   I went through
the actual assembly code, and matched what I think the code is doing
with what diacom reports it is doing, and everything seems to match.
I also made some substantial changes on how the integrators/BLMS
interact.   Before when the BLMS were being changed, the integrators
were not being adjusted, and with the VE tables being off this causes
things to oscillate over 30-60seconds before getting the mixture
right, I added code so that when the BLM is raised the integratros are
lowered by 2, and if the BLM is lowered the integrator is raised by 2
to maintain the same fuel mixture.  This resulted in the mixture being
right much faster.   The fuel usage code was pretty clear in that 2
int steps are equal to 1 blm step.  I also adjusted my BLMS to be 128
at wot, I wanted full control of the fuel and to be able to get
consistant fuel from run to run.

I also remember others running the buick turbo V6's saying that on
that car it used the BLM, and did not set it to 128 if it was lean, my
car is later than the buick V6's so I would figure it was a fix to
keep GM from having to replace as many engines from going lean at WOT
and burning pistons.

				Roger
				93 Z28