1982 MAP Sensor
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
A Manifold Absolute Pressure (MAP) sensor is a piezoelectric cell. What a piezo cell does is convert a mechanical stress into a voltage by using the properties of some materials (usually crystals) to react in this way.
A MAP sensor is reading the pressure in the intake manifold and sending the computer a voltage reference so the computer has an idea of engine load. Under low throttle angles -like at idle or in cruise- the manifold pressure would be fairly high (high Hg or high vacuum). The MAP would be telling the computer the engine is under a light load and does not need much fuel.
If the MAP sensor failed, the computer would not have a load reference and would not be able to match the engine's fuel needs. Depending upon the built-in error handlers, the engine may run lean or rich since the defaults usually reference a lookup table with just basic references. Similar to Alpha-N controls where there may be only a throttle position and rpm input. Certainly not substantial enough information for an engine that sees wide variations outside of these two inputs, but the engine will run and get you home.
MAP sensors are easy enough to test outside of sophisticated test equipment as all you need is a hand-held vacuum pump and a DVOM to read the voltage changes v. vacuum.
A MAP sensor is reading the pressure in the intake manifold and sending the computer a voltage reference so the computer has an idea of engine load. Under low throttle angles -like at idle or in cruise- the manifold pressure would be fairly high (high Hg or high vacuum). The MAP would be telling the computer the engine is under a light load and does not need much fuel.
If the MAP sensor failed, the computer would not have a load reference and would not be able to match the engine's fuel needs. Depending upon the built-in error handlers, the engine may run lean or rich since the defaults usually reference a lookup table with just basic references. Similar to Alpha-N controls where there may be only a throttle position and rpm input. Certainly not substantial enough information for an engine that sees wide variations outside of these two inputs, but the engine will run and get you home.
MAP sensors are easy enough to test outside of sophisticated test equipment as all you need is a hand-held vacuum pump and a DVOM to read the voltage changes v. vacuum.
What he said!
