[Diy_efi] MAP Sensor

[Tony Bryant]

On Wed, 24 Jul 2002 17:00, you wrote:
> Hi,
>
> Could somebody give me a quick rundown as to how an engine determines
> "load" ?
>

"Load" is undefinable, unmeasurable, and irrelevent. 

What matters is the engine is consuming a certain amount of air each cycle, 
and therefore needs a proportional amount of fuel put with it.

The three methods of detemining this amount of air are :

- MAF (Mass air flow) : measure airflow mass or volume rate going into 
engine, divide by cylinders and RPM hence get a air mass per cylinder per 
cycle.

or

- measure MAP (manfold absoulte pressure), and (as a first approximation) 
assume that in each cycle each cylinder will gulp a volume of air equal to 
its displacement volume, which is translatable to a mass via the gas laws : 
PV=nRT, P is of course the MAP. 

In reality the assumption that the cylinder will grab a volume of air equal 
to its displacement isn't a good assumption, so you end up needing a software 
table to correct for this lousy assumption.

or

- use throttle plate angle and RPM to index a lookup table, but this method 
will drive you insane for a variety of reasons I'm not going into today. 
(this method is called N-alpha)


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