Toyota Celica 1986-1993 Repair Guide

Vacuum Sensor

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The vacuum sensor, also known as the Manifold Absolute Pressure (MAP) sensor, converts a vacuum signal from the intake manifold to an electrical signal returned to the ECU. This signal is used to determine basic injection duration and basic ignition advance angle. The sensor does not use atmospheric pressure; rather, it senses the absolute pressure within the intake manifold. Since it is not affected by atmospheric pressure changes, the ECU can maintain accurate fuel metering under all weather and altitude conditions. This sensor is found on the 4A-FE and 5S-FE engines.

TESTING





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Fig. Fig. 1 Testing vacuum sensor source voltage4A-FE and 5S-FE engines



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Fig. Fig. 2 Testing vacuum sensor5S-FE engines



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Fig. Fig. 3 Testing vacuum sensor4A-FE engines

  1. Disconnect the vacuum sensor connector.
  2.  
  3. Turn the ignition switch On .
  4.  
  5. Measure the voltage between terminal VC and E2 of the vacuum sensor connector.
  6.  
  7. The voltage should read 4.5-5.5 volts. If not as specified, check the ECU wiring and the ECU.
  8.  
  9. Turn ignition switch Off and reconnect the sensor.
  10.  
  11. Disconnect the vacuum hose of the intake manifold (chamber) side.
  12.  
  13. Turn the ignition switch On .
  14.  
  15. Connect a voltmeter to terminals PIM and E2 of the ECU, then record the voltage at ambient atmospheric pressure. Apply vacuum to the sensor in increments and record the voltage drop.
  16.  
  17. The voltmeter should read:

    0.3-0.5 volts3.94 in. Hg
     
    0.7-0.9 volts7.87 in. Hg
     
    1.1-1.3 volts11.8 in. Hg
     
    1.5-1.7 volts15.8 in. Hg
     
    1.9-2.1 volts19.7 in. Hg
     

  18.  
  19. If not as specified, repair the wiring to the sensor or replace the sensor.
  20.  

 
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