MAF vs MAP

[Gary W Harris]

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> MAF sensors can handle all the transients you can throw at them
> provided they're set up properly, ie, they're sampled correctly and
> you have some form of manifold filling compensation.  I suspect that
> the additional MAP sensor is for added functionality, perhaps EGR
> control or maybe something else.

"sampled correctly and you have some form of manifold filling
compensation"  -- here, here!  Thanks for including that
short yet very important statement.

Ford currently uses a separate delta pressure gauge, dedicated
to the EGR system, to estimate EGR flow rate.

Speaking of EGR, it highlights a disadvantage of a MAP-based
system for determining inducted air.  A MAP sensor measures
the pressure of the gas in the intake manifold.  Unfortunately,
that's not the same thing as the partial pressure of the
air in the manifold under all conditions.  So, in addition to
compensation for volumetric efficiency, the ideal gas law
estimate must be adjusted for EGR.
 
--In fact, there are extensive look-up tables in the GM ECU's to compensate for 
the flow and mixture dilution due to EGR.  All must be accounted for...
GH


Anthony Tsakiris


Abbreviations:
EGR = exhaust gas recirculation
MAP = manifold absolute pressure

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