C4 System

Description & Operation


This solenoid is an electro-mechanical device integral with the carburetor that regulates the air/fuel mixture according to "commands" from the ECM.

One terminal of the MC solenoid is connected to 12 volts (battery voltage) and the other terminal is connected to the ECM. The ECM functions as an on/off switch to provide either a ground for current to flow through to energize the solenoid or an open circuit to deenergize the solenoid. The ECM switches the MC solenoid ten times per second.

When the MC solenoid is energized, the needle is inserted into the jet and the result is a lean air/fuel mixture. When the solenoid is de-energized, the needle is withdrawn from the jet and the result is a rich air/fuel mixture.

The effective or average air/fuel mixture is determined by the length of time the solenoid is either energized or de-energized (dwell) during each on/off cycle.