Learning mode (was Re:Sensor Questions?)

[Zublin, Bryan (SD-MS)]

Steve Ravet wrote:

>But if an O2 sensor is available, the SD tables can be updated as the ECM
>learns lean or rich conditions.  That is the BLM (block learn mode) that
>Scott Sealander referred to.  BLM is basically a percentage that the pulse
>width is modified by.  IF you add headers, BLM increases pulse width across 

>the board, and this is still used even in open loop mode.  So an SD system
>is capable of learning about modifications.

At low flow rates / low load conditions, this makes sense.  However, at 
higher loads and wide open throttle, how is the ECU going to learn that the 
volumetric efficiency has changed?  It would have to lean out the mixture to 
stochiometric, which is very dangerous under full throttle conditions.  The 
O2 sensor basically reports that the a/f ratio is above or below 
stochiometric, so to get any useful info (ie. learn), the engine would have 
to be closed loop.  From what I've read in the efi books, the engine *never* 
runs closed loop when at wide open throttle.

Bryan Zublin
bzublin at gi.com