When you're motor is idling the is a vacuum on the MAP sensor, my question is as the throttle is opened up and the motor is reved up is more vacuum applied or less? Does the value in millibar go up or down? I know that as the motor is opened up that the signal voltage increases but i was just wondering which way the vac works. Thanks in advance.

 

Just reving the motor won't change the readings all that much. Putting the engine under a load increases manifold pressure while decreasing vacuum. When vacuum (negative figure) reaches 0 anything above that is boost (of course it would never get that far w/o FI.

 

Cool that's exactly what i needed. So idle has vac. Open throttle under load nears 0.