Sensor Questions?

[John T Stein]

On Friday Jan 26, "SRavet" wrote the following in response to a 
request to contrast MAF vs. MAP sensor-based systems:



> The difference is that MAF is more complicated, but is more tolerant of 
> engine modifications.  MAP (or SD, speed density) use a pre-calculated 
> volumetric efficiency value.  Basically, rpm determines the volume of air 
> moving through the engine, and the pressure determines the amount of oxygen 
> in that volume.  The computer then injects the proper amount of fuel.  If 
> you increase the breathing ability of this engine (headers or intake modes, 
> etc), the computer doesn't know about it and will inject too little fuel.
> 
> MAF systems are really SD based, but the computer is able to modify the 
> injector on time based on the reading from the MAF sensor.  It is much more 
> tolerant of future engine modifications without requiring the prom to be 
> updated.
> 
> Steve Ravet
> sravet at bangate.compaq.com
> Baby you're a genius when it comes to cooking up some chili sauce...

I have heard this discussion of the "shortcomings" of MAP-based 
systems before and have always assumed that as the engine management 
computer observed a long-term lean condition (from the O2 sensor readings), it 
would adjust the injector "on" time to correct, thereby accommodating 
any changes to engine volumetric efficiency brought about by engine 
hardware modifications.  In the case of a GM system, I would expect 
the block learn values to be above nominal (128). 

Is this assumption correct, or have I credited the engine computer
with too much "intelligence"?? 

John