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

[Richard Wakeling]

Hi Larry,

Kurek, Larry wrote:
> 
> Guys:
> 
> There is a major debate going on the F-body lists concerning HP gains from
> "porting" the stock MAF. I am arguing that the HP gains being shown on the
> dyno (7-10hp), are the result of lean out since the MAF is now out of
> calibration and NOT due to the increased airflow. I think the stock MAF
> flows around 650-700CFM, which on a NA 350 is MORE than adequate. Also, what
> I am arguing, and has been proven by a few list members, is that this gain
> is short term, since the PCM will 'relearn" the correct fuel trim values
> from the O2 feedback, and adjust the mixture accordingly. So, any leanout
> effect will be compensated for by additional fuel and you will be back to
> zero gain. One list member has argued that any effect of this learning will
> not be applied at WOT since the computer is not in learn mode. Doesn't the
> PCM just use the last value in the BLM to adjust WOT fuel? Don't you need to
> force this BLM cell to 128 (with custom programming) when going WOT to
> negate any learning effect?

	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)
> 
> Finally, and this is my major question to this list. Has anyone ever
> considered, or actually built, a voltage adder/subtracter for "massaging" of
> the O2 signal? From what I can tell, this is the ONLY way to seriously
> impact fuel curves (short of reprogramming) over the long term AND at WOT.
> I'm sure you could build something that takes an input voltage and adds or
> subtracts, say 0-100mv, and send this signal to the PCM. A nice dial setup
> (adjustable pot) could vary the range (I would assume a +/- 100mv range
> would work), and have the ability to synchronize two inputs (for a
> left/right O2 setup) with the one dial. Doable? If so, how? comments?
> 
> TTYL!
> 
> Larry