[Diy_efi] MAP Sensor

[Djfreggens at aol.com]

ok heres the very short version 

 engines create vacum with the throttle closed ie lots of space in the 
cylinders not being filled with air. 
 when the throttle is open there is less vacum ie more air entering the 
engine hence forth more load 

  ok now that is straight heres how a map sensor works. 

  when there is alot of vacum ie no load the map has a very low output 
voltage. 
  when there isn't much vacum ie more load  ma voltage goes up 

  to make things a hair more confusing 

 maps work form 0-5 votls positive. now say at idle no load an engine has a  
map output of say 2.0 volts at full throttle the same map sensor may have an 
output of 4.5 volts. 

  now the ecu see this volatge and covnerts it through a a/d (analog to 
digital) chip or channel or converter what ever the individual ecm may do to 
turn it into a digital signal. this digital signal is read by the proccesor 
in terms of HG which is vacum or KPA which is air pressure 

  now to make things more intersting we can go into a very breif abrigded 
version of hwo the proccesor uses and store this info. 

   in every ECU there is an eprom or some sort of memory where the proccesor 
looks for information on how to interprett and uses various engine sensor 
readings. 

  in a speed density setup IE map sensor there is almost always a VE table. 
The Ve table is Volumetric Efficency. this is the table that the ecu uses to 
make uses of its map signal to determin the proper amount of feul to be 
sprayed inot the injector. 
 they map also effect spark timing as well. it has influence and cotrl over 
lots of paramters in the engine to complex to dive into here here is a link 
to get a little more familiar with the concepts.


http://www.geocities.com/MotorCity/Shop/9938/bruce/prog_101.html 

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