See Figures 1 and 2
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 liquid fuel.
The computer looks at alternator terminal L to determine if the engine is running and also watches the engine's coolant temperature. If the engine is running and the coolant temperature is below 109°F (43°C), the computer energizes the cold mixture heater relay, which in turn applies battery voltage 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 131°F (55°C) the CMH relay is de-energized and the heater elements turn off.
Cold Mixture System Operation
- Start the engine. The coolant temperature must be below 109°F (43°C).
- Using a voltmeter, check that there is voltage between the positive (+) terminal (white/red wire) and the ground.
- Allow the engine to warm up and check the OHM with the engine warm. The coolant temperature should be above 131°F (55°C).
- Using a voltmeter, check that there is NO voltage. If no problem is found with this inspection, the system is working properly.
- Unplug the wiring connector.
- Using an ohmmeter, check the resistance between the heater terminals. The resistance should be 0.5-2.0 -. Readings outside this range require replacement of the heater element.
- Replug the wiring connector.
- 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.
The relay is located under the air intake hose behind the battery.
- Apply battery voltage to terminal No. 1 and ground terminal No. 2. Use the ohmmeter to check for continuity between terminals 3 and 4.