GM Corvette 1984-1996 Repair Guide

Manifold Absolute Pressure (MAP) Sensor

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OPERATION



The MAP sensor measures the changes in intake manifold pressure, which result from engine load/speed changes and converts this information to a voltage output. The MAP sensor reading is the opposite of a vacuum gauge reading: when manifold pressure is high, MAP sensor value is high and vacuum is low. A MAP sensor will produce a low output on engine coast-down with a closed throttle while a wide open throttle will produce a high output. The high output is produced because the pressure inside the manifold is the same as outside the manifold, so 100 percent of the outside air pressure is measured.

The MAP sensor is also used to measure barometric pressure under certain conditions, which allows the PCM to automatically adjust for different altitudes.

The MAP sensor changes the 5 volt signal supplied by the PCM, which reads the change and uses the information to control fuel delivery and ignition timing.

TESTING



See Figures 1 and 2

  1. Visually check the connector, making sure it is properly attached and all of the terminals are straight, tight and free of corrosion.
  2.  
  3. With the ignition ON , check the voltage between terminals A and B. It should be above 4 volts. Apply 15 in. Hg of vacuum at the MAP vacuum port and check the voltage again. The voltage should be 2 volts now.
  4.  



Click image to see an enlarged view

Fig. Fig. 1: Manifold Absolute Pressure (MAP) sensor circuit

When pumping up and releasing the vacuum, check to make sure the voltage readings are smooth. When applying vacuum to the sensor, the change in voltage should happen instantly. A slow change in voltage could point to a faulty sensor.



Click image to see an enlarged view

Fig. Fig. 2: MAP sensor voltage specifications

  1. If the sensor voltage is not within specification, check for a 5 volt reference at terminal C. If the reference signal is found, the sensor is faulty.
  2.  
  3. If the sensor and circuits are functional, the PCM may be faulty.
  4.  

REMOVAL & INSTALLATION



Except VIN J Engines

See Figure 3

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the MAP sensor electrical connector.
  4.  
  5. Unfasten the 2 sensor hold-down bolts, then remove the MAP sensor from the intake manifold.
  6.  



Click image to see an enlarged view

Fig. Fig. 3: Exploded view of the MAP sensor-1994 VIN P shown

To install:

If equipped, lightly coat the seal on the MAP sensor with clean engine oil.

  1. Install the MAP sensor on the intake manifold.
  2.  
  3. Install the retaining bolts and tighten to 50 inch lbs. (6 Nm).
  4.  
  5. Attach the sensor electrical connector.
  6.  
  7. Connect the negative battery cable.
  8.  

VIN J Engines

See Figure 4

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the sensor hold-down bolts.
  4.  
  5. Remove the protective cover.
  6.  
  7. Detach the electrical connector and unplug the vacuum hose.
  8.  
  9. Remove the MAP sensor.
  10.  



Click image to see an enlarged view

Fig. Fig. 4: Location of the MAP sensor-VIN J engines

To install:
  1. Instlal the MAP sensor.
  2.  
  3. Attach the vacuum hose and electrical connector.
  4.  
  5. Install the protective cover.
  6.  
  7. Install the hold-down bolts and tighten to 50 inch lbs. (6 Nm).
  8.  
  9. Connect the negative battery cable.
  10.  

 
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