This system is only used on the 4A-F engines.
The Cold-Mixture Heater (CMH) system reduces cold engine emissions and improves driveability during engine warm-up. The intake manifold is heated during cold engine warm-up to accelerate vaporization of the fuel.
If the engine is running and the coolant temperature is below a predetermined limit, the computer energizes the cold mixture heater relay. This in turn allows battery voltage to be applied to the cold mixture heater. The CMH is a Multi-element heater ring that is mounted between the carburetor base and the intake manifold. Once the coolant temperature exceeds a certain limit, the CMH relay is de-energized and the heater elements turn off.
Mixture Heater Element
- Unplug the wiring connector.
- Using an ohmmeter, check the resistance between the heater terminals. The resistance should be 0.5-2.2 ohms. Readings outside this range require replacement of the heater element.
- Replug the wiring connector.
This relay is located on the left fender apron.
- Check that there is continuity between the No. 1 and 2 terminals. Check that there is NO continuity between the No. 3 and 4 terminals.
- Apply battery voltage to terminal No. 1 and 2. Use the ohmmeter to check for continuity between terminals 3 and 4.