Mixture Control Solenoid: Description and Operation

The ECM controls the air/fuel mixture through the MC solenoid ground circuit--actuating the metering rods.
- When the MC solenoid is energized (down position), fuel flow is reduced providing leaner mixtures.
- When the solenoid circuit is open (up position), more fuel is allowed to flow, providing richer mixtures.

The ECM cycles the MC solenoid "ON and OFF" at a fixed rate of 10 times per second.
The air/fuel mixture is adjusted by varying the amount of time the solenoid is energized per cycle--solenoid dwell.

NOTE: Solenoid dwell can be read using most dwell meters. If engine operation changes when a dwell meter is connected to the mixture control solenoid use a different meter. Meters with three leads are more likely to be able to measure solenoid dwell correctly than those with two leads.