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    GM Camaro/Firebird 1993-1998 Repair Guide

    Manifold Absolute Pressure (MAP) Sensor

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    OPERATION



    See Figure 1

    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.



    Click image to see an enlarged view

    Fig. Fig. 1: Typical MAP sensor-except 1998 5.7L engine

    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 2 and 3

    1. Visually check the connector, making sure it is connected properly 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. 2: 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. 3: 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



    See Figures 4 through 10

    1. Disconnect the negative battery cable.
    2.  
    3. Detach the MAP sensor electrical connector.
    4.  



    Click image to see an enlarged view

    Fig. Fig. 4: Unplug the Manifold Absolute Pressure (MAP) sensor electrical connector

    1. For the 3.4L and 1993-97 5.7L engines, perform the following:
      1. Remove the retaining bolts locking tabs and pull the sensor partially out.
      2.  
      3. Unplug the vacuum connection, then remove the sensor from the vehicle.
      4.  

    2.  



    Click image to see an enlarged view

    Fig. Fig. 5: Remove the MAP sensor retaining bolts ...



    Click image to see an enlarged view

    Fig. Fig. 6: ... then remove the MAP sensor from the intake plenum

    1. For the 3.8L engine, carefully bend the locking tabs that hold the MAP sensor to the manifold vacuum source, just enough to remove the sensor. Pull the sensor straight out of the vacuum source.
    2.  
    3. For the 1998 5.7L engine, twist the MAP sensor forward, in order to release the sensor from the retainer, then pull the sensor upward to remove it from the vehicle.
    4.  



    Click image to see an enlarged view

    Fig. Fig. 7: MAP sensor location-3.4L engine



    Click image to see an enlarged view

    Fig. Fig. 8: Location of the MAP sensor-3.8L engine



    Click image to see an enlarged view

    Fig. Fig. 9: The MAP sensor on the 1993-97 5.7L engine is retained by two bolts



    Click image to see an enlarged view

    Fig. Fig. 10: MAP sensor mounting-1998 5.7L engine

    To install:

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

    1. For the 1998 5.7L engine, install the MAP sensor, then push the sensor down in order to engage the sensor and the retainer.
    2.  
    3. For the 3.8L engine, perform the following:
      1. Make sure the seal is installed on the MAP sensor and the seal is not damaged.
      2.  
      3. Install the MAP sensor to the manifold vacuum source. Make sure the locking tabs engage to hold the sensor to the vacuum source.
      4.  

    4.  
    5. For the 3.4L and 1993-97 5.7L engines, perform the following:
      1. Position the MAP sensor to the intake plenum and attach the vacuum line.
      2.  
      3. Install the retaining bolts.
      4.  

    6.  
    7. Attach the sensor electrical connector.
    8.  
    9. Connect the negative battery cable.
    10.  

     
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