MAP Questions...

[atsakiri at ford.com]

> This is what I know. The MAP sensor will give me a reading on the manifold 
> vacume. I can correct this with a temp sensor to give the amount of air that 
> the
> engine desires. I was wondering how I would go about using this sensor to 
> determine how much air I need. 

That's got me a bit confused.  Could you restate that part?


>      Is a MAP system just mapped out? Like an array. Where temp is one 
> demension, Vac is the second dimesnion and the array value is the fuel. Take 
> this data for several points on the RPM curve then when the engine is running
> have it integrate the curve data and find the appropriate value for fuel?

Isn't the goal of most MAP-based systems the same as that of MAF-based 
systems, namely to estimate the mass of air inducted into the cylinder?
For a MAP-based system, this would be an application of the ideal gas
law with the addition of a volumetric efficiency term.

   pV = mRTe

           where   p = manifold absolute pressure
                   V = cylinder displacement
                   m = air mass inducted
                   R = gas constant
                   T = absolute temperature
                   e = volumetric efficiency
                                                .   .          .
This could also be expressed in rate terms ... pV = mRTe where V is
determined by engine speed.

This is a very simple approach.  I think the difficulties arise in
determining volumetric efficiency, which varies with temperature, 
barometric pressure (mainly an exhaust-side effect), etc.  The maps
you speak of would be of volumetric efficiency and various 
correction factors.

As to size of the sensors, I've seen them at about 
80 mm x 50 mm x 15 mm.



Anthony Tsakiris

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The opinions expressed are my own and not necessarily those of my employer.