An electric assist choke is used to more accurately match the choke operation to engine requirements. It provides extra heat to the choke bimetal spring to speed up the choke valve opening after the underhood air temperature reaches 95°F ± 15°F (35°C). Its purpose is to reduce the emission of carbon monoxide (CO) during the engine's warmup period.
A special AC terminal is provided at the alternator to supply a 7 volt power source for the electric choke. A thermostatic switch within the choke cover closes when the underhood air temperature reaches 95°F ± 15°F (35°C) and allows current to flow to a ceramic heating element. The circuit is completed through the choke cover ground strap and choke housing to the engine. As the heating element warms up, heat is absorbed by an attached metal plate which in turn heats the choke bimetal spring.
After the engine is turned off, the thermostatic switch remains closed until the underhood temperature drops below approximately 65°F (18°C). Therefore, the heating element will immediately begin warming up when the engine is restarted, if the underhood temperature is above 65°F (18°C).
- Detach the electrical lead from the choke cap.
- Use a jumper lead to connect the terminal on the choke cap and the wire terminal, so that the electrical circuit is still completed.
- Start the engine.
- Hook up a test light between the connector on the choke lead and ground.
- The test light should glow. If it does not, current is not being supplied to the electrically assisted choke.
- Connect the test light between the terminal on the alternator and the terminal on the choke cap. If the light now glows, replace the lead, since it is not passing current to the choke assist.
- If the light still does not glow, the fault lies somewhere in the electrical system.
If the electrically assisted choke receives power, but still does not appear to be functioning properly, reconnect the choke lead and proceed with the rest of the test.
- Tape the bulb end of a thermometer to the metallic portion of the choke housing.
- If the electrically assisted choke operates below 55°F (13°C), it is defective and must be replaced.
- Allow the engine to warm up to between 80°F and 110°F (27-43°C); at these temperatures the choke should operate for about 1 1 / 2 minutes.
- If it does not operate for this length of time, check the bi-metallic spring to see if it is connected to the tang on the choke lever.
- If the spring is connected and the choke is not operating properly, replace the cap assembly.