IGNITION
Page 2A-22 90-884294 OCTOBER 2001
Manifold Absolute Pressure (MAP) Sensor
The MAP sensor is located on top of the air plenum. The ECM regulates fuel flow, in part,
based on manifold absolute pressure. The MAP sensor becomes more critical in engine
running quality as the engine is operated at higher altitudes (i.e. mountain lakes). Should
the MAP sensor fail, the ECM will default to a value of approximately 14.7 psi.
The MAP sensor’s DDT readout will vary according to altitude, throttle plate opening and
barometric pressure. However, for a given location and weather conditions (I.E. altitude
and barometric pressure), the MAP sensor readout between engines should be approxi-
mately the same when the ignition key is turned to the “ON” position. For example, if two
engines indicate 15 psi when the key is turned “ON” and a third engine indicates 10 psi,
the third engine’s MAP sensor would be suspect. When the engines are started, MAP sen-
sor readout should drop. When the engines are initially accelerated, the MAP sensor
readout will drop momentarily and then begin to rise. Throttle plate opening will also affect
the MAP readout. Refer to Section 2C for correct throttle plate clearance.
The Digital Diagnostic Terminal (DDT) can be used to determined whether the MAP sen-
sor is functioning properly. As throttle is advanced, numerical value on DDT display
should increase. As throttle is retarded, numerical value should decrease indicating MAP
sensor is functioning. If numerical value does not change as throttle setting varies, MAP
sensor is defective.
NOTE: If MAP sensor is not functioning, #4 LED indicator light on DDT will be illuminated.
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59025
a-Manifold Absolute Pressure (MAP) Sensor
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