Sensor Questions?

[FIScot at aol.com]

    Subj:   re: Sensor Questions?
    Date:   96-01-29 19:16:59 EST
    From:   SRavet at bangate.compaq.com

    [text deleted]

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

 >  John, you are correct, my description above was a little simplistic.
 >  As long as the ECM is in closed loop, it will adapt (within the block
 >  learn limits).  If you aren't closed loop, though, pre-programmed
 >  values are used which will result in a lean condition.
 >  Steve Ravet

    In the GM ECM's, whether you are in CL or not, the ECM is running
    through the same 'preprogrammed' code.  Closed loop adds the ability
    for the BLM to learn.  If not in closed loop, the BLM is still used,
    and if not altered by a complete power off, will still correct the fuel
    mixture from what it has learned.

    Part of the equation is:

    Fuel = Integrator * BLM * (rest of fuel calculation)

    In open loop, the integrator is set to neutral.  The BLMs are whatever
    has been learned, so the fuel correction still goes on.  One caveat is
    that some ECMs will check (and reset) the BLMs at ignition power on for
    a tighter limit than is allowed during normal operation.  The same
    things happen when in PE, i.e., the integrator goes neutral, and the
    BLM is whatever has been learned.

    The only thing that closed loop adds is the ability to learn, and
    the integrator (with help) keeps the fuel about 14.7 AFR.

    Scot Sealander   FIScot at aol.com