Beretta L4-121 2.0L (1987)
CIRCUIT DESCRIPTION
The Manifold Absolute Pressure (MAP) sensor measures manifold pressure and sends that signal to the ECM. The MAP sensor is mainly used to
calculate engine load, which is a fundamental input for spark advance and fuel calculations. The MAP sensor is also used to determine barometric
pressure.
TEST DESCRIPTION
Numbers below refer to circled numbers on diagnostic chart:
1. Checks MAP sensor output voltage to the ECM. This voltage, without the engine running represents barometric pressure to the ECM. Comparison
of this BARO reading with a known good vehicle with the same sensor is a good way to check accuracy of a "suspect" sensor. Readings should be
the same ± 0.4 volt.
2. Applying 34 kPa (10" Hg) vacuum to the MAP sensor should cause the voltage to decrease 1.2 volts from the voltage read in step 1. When
applying vacuum to the sensor the voltage change should be immediate. If the voltage changes slowly the sensor is bad.
3. Carefully check the vacuum hose for leaks or restrictions. No other devices should be connected to the hose.
