ISUZU Amigo/Pick-ups/Rodeo/Trooper 1981-1996

Thermostatically Controlled Air (TCA) Cleaner System

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OPERATION



See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: TCA system operation

The TCA functions to maintain ambient air air temperature at an optimum level so that the fuel/air ratio remains constant. This ensures fuel combustion and reduces pollutant emissions. The TCA system is mounted on the air cleaner. It consists of a vacuum motor, hot air control damper and an Inlet Temperature Compensator (ITC) valve.

When the engine is running, there is no vacuum signal at either the vacuum motor or the ITC valve. In this condition the vacuum motor spring closes off the passage from the hot air duct. On a cold start, the ITC valve delivers maximum vacuum to the vacuum motor which moves the hot air control damper to the fully open position. This closes the ambient air passage and opens the hot air duct. If the engine speed increases, the system vacuum level will drop allowing the diaphragm spring to overcome the vacuum force and push the hot air control damper to the fully closed position.

When the engine is running under normal conditions, the ITC valve closes the passage to the intake manifold and opens the passage to the from the air cleaner to the vacuum motor. As fresh air is fed to the vacuum motor, the diaphragm spring forces the air control valve to close off the hot air duct and open the ambient air passage.

During conditions of extended idling, hill climbing or high speed driving, there is a substantial increase in engine and engine compartment temperatures. This results in an excessive amount of fuel vapor entering the intake manifold, causing an over-rich mixture. The over-rich mixture causes rough idling and increased CO emissions. To prevent this, the ITC valve opens the passage from the air cleaner to the intake manifold. Fresh air is allowed to enter the intake manifold and lean out the mixture.

TESTING



Vacuum Motor
  1. Remove the air cleaner.
  2.  
  3. Unplug the vacuum hose from the motor.
  4.  
  5. Check that the hot air flap is completely closed.
  6.  
  7. Apply vacuum to the motor. Check that the flap opens and is able to hold a vacuum.
  8.  
  9. Replace the motor if necessary.
  10.  

Thermo Sensor

See Figure 2



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Fig. Fig. 2: The thermo sensor is positioned next to the inlet temperature compensator

  1. Remove the air cleaner.
  2.  
  3. Apply a vacuum to the sensor. If the ambient air temperature is below 86°F (30°C) on 2.8L and 3.1L engines or 100-111° F (38-44° C) on other engines, it should hold a vacuum.
  4.  
  5. With a hair drier, heat the sensor to above 86°F (30°C) on 2.8L and 3.1L engines or 100-111° F (38-44° C) on other engines. The sensor should now bleed off the vacuum.
  6.  
  7. Replace the sensor if necessary.
  8.  

Inlet Temperature Compensator

See Figure 3



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Fig. Fig. 3: Testing the inlet temperature compensator

This is not used on 2.8L and 3.1L engines.

  1. Remove the air cleaner.
  2.  
  3. Blow air through the sensor hose. If the ambient air temperature is below 115°F (46°C), air should not pass.
  4.  
  5. With a hair drier, heat the sensor to above 115° F (46°C). The sensor should now be able to pass air.
  6.  
  7. Replace the sensor if necessary.
  8.  

 
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