GM Prizm/Nova 1985-1993 Repair Guide

Automatic Choke

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OPERATION



See Figures 1 and 2

The automatic choke system temporarily supplies a rich air/fuel mixture to the engine by closing the choke valve (plate) when the engine is cold. At cold temperatures with the ignition switch ON but the engine not running, there is no voltage supplied from the alternator's L terminal at the choke heater. The bimetal choke spring is contracted, closing the choke valve.



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Fig. Fig. 1: Choke system components

As soon as the engine is running, the L terminal supplies voltage to the choke heater. The heat generated is transferred to the bimetal spring causing it to unwind-opening the choke valve. This helps provide a relatively quick transition between the rich (cold) setting to the normally open position when the engine no longer requires the rich air/fuel mixture.

TESTING



Automatic Choke
  1. Allow the choke valve to close.
  2.  
  3. Start the engine.
  4.  
  5. Check that the choke valve begins to open and the choke housing is heated.
  6.  

Heating Coil
  1. Unplug the wire connector.
  2.  
  3. Measure the resistance with an ohmmeter. The resistance should read: 19-24 ohms 68°F (20°C). Allow for slight variations due to temperature differences.
  4.  



Click image to see an enlarged view

Fig. Fig. 2: Choke system operation chart

 
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