how does the VAFC manipulate the correction % for fuel? what values or readings is it changing to affect the amount of fuel +/- injected.

 

It interupts the manifold absolute pressure sensor signal to the ecu.

If you put in +5% for fuel, it changes the MV reading of this sensor to tell the ecu there is 5% more air.

 

The VAFC lengthens and shortens the injector pulse duration, correct?

 

Indirectly. It just changes what the ecu sees as air pressure.

If you tell the VAFC to add 5% it simply interupts the MAP sensor signal and tells the ecu there is 5% more air (in mv).

As a result, the ecu dumps more fuel by lengthening pulse width.

 

by interupting the MAP signal and changing it to aquire a fuel +/- does that cause a change to any thing else?