Mixture Control Solenoids

The Mixture Control Solenoid alters the air-fuel mixture in the electromechanical, or computer (ECU) controlled, carburetor.

Based on changing inputs from sensors, such as MAP or Manifold Absolute Pressure and O2 or Oxygen Sensor, the computer cycles the Mixture Control Solenoid On and Off several times a second.

If the ECU sends a lean signal, the signal voltage to the solenoid remains in the On position more than the Off position, causing less fuel to pass through the solenoid valve and the mixture becomes leaner.

If the computer sends a rich signal, the signal voltage to the solenoid cycles in the Off position more than the On, and the mixture becomes richer.

NOTE: all computerized carburetor systems are different. Referring to the manufacturer’s service manual is highly recommended.

Symptoms of a failing Mixture Control Solenoid may include
• Rich mixtures
• Catalyst odor
• No start conditions
• Check Engine light on