The MAP sensor is a key sensor as it senses the engine load. the sensor's generated signal is proportional to the amount of vacuum in the intake manifold. the ECU then uses the information to adjust ignition timing and fuel enrichment.
During my experiment i have wired up a MAP sensor with a 5 Volts feed and earth and the following are the return voltage from the third wire. I have used a mity-vac to apply vacuum to the map sensor, voltage return in relation to the vacuum applied is shown in the plot below:
Does the MAP sensor match the manufacturer specifications, why or why not?
Yes i does match the manufacturer specifications, because the higher the vacuum the higher the voltage.
Does a MAP sensor read a vacuum or pressure?
The MAP sensor use a perfect vacuum as a reference pressure .
Explain the internal operation of this sensor and why the output voltage changes?
The MAP sensor voltage signal is higher when intake manifold pressure is higher, the MAP sensor voltage sensor is lower when intake manifold pressure is lower on de-acceleration with throttle close.
As in the figure illustrated above on 25 Hg Vacuum pressure the voltage was 5 Volts.
In the MAP sensor there is a silicon chip which is mounted inside a reference chamber. Reference pressure is on one side of the chip which is either a perfect vacuum or a calibrated pressure depending on the application. As the pressure changes the silicon chip changes its resistance as well. When the silicon chip fixes with the change in pressure, the electrical resistance of the chip changes which results in voltage signal alteration. The voltage signal is interpreted by ECM as a pressure and any change in the voltage signal means there was a change in pressure.
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