MEFI Fuel Injection
Manifold Absolute Pressure Sensor (MAP)
MEFI 1 and 3
8.1L
The Manifold Absolute Pressure (MAP) sensor is a pressure transducer that measures changes in the intake manifold pressure. It takes this pressure and converts it into a voltage signal. The output is directly proportional to the intake manifold pressure. (inverse to manifold vacuum) A closed throttle will result in a low voltage. (low pressure) Wide open throttle will produce a high voltage. (high pressure) The ECM uses the “key on” voltage to read barometric pressure which sets the fuel curve for the engine while it is running. This baro read voltage is critical to engine operation. If the “key on” baro reading is lower than the actual barometric pressure (due to a problem in the MAP or MAP circuit), then the engine will be starved for fuel. Conversely, if the key on baro reading is higher than the actual barometric pressure, the engine will receive too much fuel through out the entire range of engine operation. The only ways to validate the barometric pressure reading from the MAP is to compare the ECM’s baro reading to a barometer or compare it to a known good engine in the same area.
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