Fuel Control

California pickups are equipped with "feedback" carburetors which contain an electrically-operated Mixture Control (M/C) solenoid. The M/C solenoid operates single or dual metering rods in float bowl of carburetor.

A metering rod supplements fuel supply to idle and main systems, varying air/fuel ratio within a precalibrated range. The M/C solenoid also controls air/fuel ratio through use of an idle air bleed circuit that operates in conjunction with metering rod(s).

The ECM reacts to input from data sensors by constantly adjusting air/fuel mixture to maintain efficient engine performance. ECM controls M/C solenoid by providing a ground for solenoid.

When solenoid is energized, fuel flow through carburetor is reduced, providing a leaner mixture. When solenoid is de-energized, fuel flow through carburetor is increased, providing a richer mixture. The solenoid cycles (turns on and off) 10 times per second.

During closed loop operation, the ECM adjusts fuel mixture in response to signals received from oxygen sensor. Under certain operating conditions, ECM may ignore inputs from some sensors and use pre-programmed data to operate engine.

During cold engine starts (engine speed below 200 RPM), M/C solenoid is turned off by ECM so that a rich mixture can be provided. Certain operating conditions cause ECM to ignore oxygen sensor signals. CCC system then operates in open loop mode.