Volvo 240/740/760/780/940/960 1990-1998

Manifold Air Pressure Sensor

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OPERATION



The most important information for measuring engine fuel requirements comes from the pressure sensor. Using the pressure and temperature data, the ECM calculates the intake air mass. It is connected to the engine intake manifold through a hose and takes readings of the absolute pressure. A piezoelectric crystal changes a voltage input to an electrical output which reflects the pressure in the intake manifold.

Atmospheric pressure is measured both when the engine is started and when driving fully loaded, then the pressure sensor information is adjusted accordingly.

The pressure sensor terminal has 3 connectors A, B and C. A is ground, B carries the output signal to the control unit and C provides the pressure sensor with 5 volts of current from the control unit. The output varies between 0.5-5.0 volts depending on intake manifold pressure. When the engine is not running, atmospheric pressure will register at full potential. The sensor is sensitive to electrical disturbances, therefore it is protected by a metal cover. The signal strength should be about 4.4 volts at atmospheric pressure.

TESTING



See Figures 1, 2 and 3

  1. Turn the key to the ON position, with the engine OFF .
  2.  
  3. Test the voltage of the sensor across terminals A and B of the sensor by backprobing the connector.
  4.  
  5. Adding controlled pressure to the vacuum port on the sensor will help to verify the sensors operation. A hand-held pump with a gauge (not a vacuum pump) or regulated air pressure can be used.
  6.  
  7. Using the chart in this section for a cross reference, check the voltage in relationship to the pressure.
  8.  
  9. If the sensor is not within specifications, replace it.
  10.  
  11. The sensor may also be checked with the engine running; at idle, the sensor should read 1.2-1.6v.
  12.  



Click image to see an enlarged view

Fig. Fig. 1: Pressure-to-voltage conversion chart for the MAP sensor



Click image to see an enlarged view

Fig. Fig. 2: MAP sensor connector terminal identification



Click image to see an enlarged view

Fig. Fig. 3: Typical MAP sensor and terminal (pin) identification

REMOVAL & INSTALLATION



  1. Disconnect the negative battery cable.
  2.  
  3. Remove the bolts securing the bracket to the firewall.
  4.  
  5. Remove the vacuum hose from the sensor.
  6.  
  7. Unplug the connector and remove the sensor.
  8.  

To install:
  1. Plug in the sensor connector.
  2.  
  3. Install the vacuum hose.
  4.  
  5. Install the sensor into place and tighten the bracket retaining bolts.
  6.  
  7. Connect the negative battery cable.
  8.  

 
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