More silly ideas-MAP

[Jeff M]

>When you consider what the engine is doing, MAP makes a lot of sense since
>what matters is the cylinder filling pressure which is maximum when MAP is
>max. Secondly referencing to zero makes sense since the atmospheric
pressure
>is liable to vary all over the MAP and you do not want the same WOT setting
>in Denver as in Miami. The zero reference point OTOH is the same no matter
>where you are. Besides the engine does not care what the outside pressure
>is, just what is in the manifold.
>      A. Padgett Peterson, P.E.


I am remembering quotes from my digital fuel research and as I recall, it
does need to know what the MAP is before the engine is started, this is the
"BARO" reading that does show up on some systems via the ALDL communications
port.  This lets the computer know what the reference point is before
deciding what is being contributed by the volumetric changes as the engine
runs, especially boosted engines.  This check for BARO is done right after
the ignition is turned to on and before it goes to start (the engine).
Besides, just before engine start up, outside is inside as far as pressures
;-}

Jeff Middaugh
tystorm at email.msn.com