Manifold Absolute Pressure Sensor / On car

Manifold Absolute Pressure Sensor

The map sensor is usually mounted on the firewall with a hose connected to the intake manifold.The map sensor is a very important sensor that sensors engine load. The sensor measures vacuum. More pressure is less vacuum and more vacuum is less pressure. At idle the vacuum is high as there is less air pressure in the engine. At open throttle there is more pressure therefore there is less vacuum in the intake manifold.

When i was testing my map sensor, i wired up a 5v supply and earth. Hooked up a multimeter to see the voltage at signal.I Then hooked up a mity-vac to the vaccum port of the map sensor. With no vacuum i got 4.8 volts at signal and as i applied vacuum with the mity-vac the voltage started to decrease. At around 70 cm Hg of vacuum the voltage got to almost .8v.

Vacuum cmHg	Voltage out
0	4.8
10	4.09
20	3.39
30	2.56
40	2.01
50	1.3
60	0.96
70	0.8

By my results its shows me that my map sensor is in good working condition and it is within the manufactures specification. My map sensor was a off a Toyota and i checked it with the toyota service manual that is posted on blackboard.

The map sensor reads vacuum to send out a voltage to the ecu. Theres is more vacuum at idle therefore its sends a low voltage telling the ecu theres less air in the inta`ke manifold. At wide open throttle there is less vacuum therefore the map sends a high voltage to the ecu. Its telling the ecu there is more pressure/air in the intake therefore the ecu adjusts injection timing and etc to give the engine optimum perfomance. 

On Car MAP Sensor

My engine had a map sensor. I back probed the signal wire of the map and connected my multimeter set to read DC volts. red probe to the signal and black probe ground. I turned the igniton on. I got a reading of 1.818V.

When i started the engine voltage dropped down to 0.541V.

When i revved the engine but just a short burst, the reading increased to 1.818v again.

When the ignition is turned the map reads the outside air pressure so we get 1.8v. As we start the engine at idle there is vacuum form the engine sucking in air so the voltage drops to 0.5v. When we are accelerating there is more air entering the intake, therefore more pressure and less vacuum so the voltage increases to 1.8 again. This voltage then tells the ecu that there is more air entering the intake so then the ecu increases the fuel into the air fuel mixture. This shows us that the readings we got was correct.

Problems that would send incorrect signal to the ecu from the MAP:

 - Vacuum leak in the intake

 - Leak on the map vacuum hose

 - The diaphram inside the map not holding vaccum.

 - poor grounding of the map ( high resistance on the ground)

 - Ecu grounding loose creating high resistance

 - corrosion on connectors