MAP sensor

[Webby]

This could be a stupid question but as I have rewired my ezefi loom here goes.
Should MAP sensor reading increase with increased vacuum or decrease?
My MAP sensor reading increases big time when I nail the throttle and then decreases to about 10 when I back off. Idle reading is about 55.
Does this sound correct?

[Webby]

Hmm further research makes me think that if wired wrong the sensor will not work at all. So I guess it was a stupid question.

[FAST Tech Maxwell]

I also replied to your email with the same response.

The MAP sensor reads in absolute kilo-Pascals or kPa. Normal atmospheric pressure at sea level measures about 101.3kPa. A perfect vacuum is 0kPA, which is the same as 29.9" of mercury.

So 55kpa at idle would be the same as 16.2" of mercury at sea level.

When you let off the throttle, the cylinders will make a lot of vacuum in the intake because they are still moving very fast. That is why you will see a surge downward in MAP.

Hope that helps.

[SoCal]

Yeah, what he said.

More vacuum = lower reading.

A crude but effective way to test the basic functioning of a MAP sensor, wiring, etc. is to suck on it. In open air, the reading should be around 100. As you put some vacuum to it, the MAP reading should go down.