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

[Roger Heflin]

On Tue, 23 Mar 1999, 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?
>
THe PCM forces the BLM to 128 if it is below 128.  Above 128 stays at
whatever value it is at (except on my computer - mine always goes to
128 at wot, couple of internal branches accidently got changed and
caused this behavior, I wonder how that happened).   If you want to
confirm yours does this, watch the blms in diacom or a simlar software
during wot, if the value was below 128 when it went wot, the value
will change to 128, if above 128 it will stay there.

 
> 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?
> 

I would not lean things out any, since the computer always goes to 128
if the BLM is below 128.  I think this is to prevent dangerous
conditions, so messing with the O2 would not be able to lean things
out more than the original 128.  If things were being richend up it
could lean it back to the stock 128.

I did not notice the MAF discussion on the fourth-gen list, but since
I don't have a MAF I probably ignored it.
 > TTYL!
> 
> Larry
> 

			Roger
			93 Z28