MAP sensors (on/ off car)

OFF CAR

The MAP sensor (manifold absolute pressure) senses how much vacuum there is inside the inlet manifold, when there is more vacuum, there is less output voltage to the ecu. when the sensor is reading a low vacuum there is a higher voltage to the ecu. When the throttle is wide open the sensor will be reading a very low vacuum because all of the pressure is being sucked into the engine, this means the manifold can not build up enough pressure to give a big reading to the ecu so it sends a small voltage, this makes the fuel injectors stay open for longer to put more fuel into the engine.

When the throttle is closed then engine is building up vacuum because not much pressure can get into the manifold, this means that the engine vacuum is sucking and the vacuum inside the manifold gets bigger creating a greater voltage to the ecu, this means the engine is at idle and will tells the injectors to stay open for only a short amount at a time to limit the fuel into the combustion chamber.

www.atspeedracing.co.uk

The Map sensor has a input for a tube where it get the vacuum from the manifold. it has 3 terminals on it (5 volt input, earth and a output voltage that it sends to the ecu)

To test this sensor i had to use a devise that creates vacuum and put it onto the vacuum tube input. I then had to give the sensor a 5 volt battery supply which i hooked up to the 5 volt terminal, i also put the negative clip of the battery supply to the earth terminal of the sensor. Once i did that i measured the voltage output with my multimeter, i set it to read around 20 volts and then placed my positive prong on the output pin of the sensor and my negative prong on the earth terminal of the sensor.

below is a picture of the devise i used to apply vacuum to the sensor:

www.autotechnique.fr

the more vacuum i applied, the less the voltage output to the ecu