Fuel Control

All models are equipped with feedback carburetors which contain an electronically operated Mixture Control (M/C) solenoid. The M/C solenoid operates a single metering rod in float bowl. Metering rod supplements fuel supplied to idle and main systems, varying air/fuel ratio within a pre-calibrated 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.

The ECM, responding to inputs from data sensors, constantly adjusts air/fuel mixture to maintain engine performance. The 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 is cycled (turned on and off) at a rate of 10 times per second.

When ECM responds to signals received from oxygen sensor to adjust fuel mixture, the C-4 system is in closed loop operation. Under certain operating conditions, the ECM may ignore inputs from various sensors and use a pre-programmed calibration control to operate the engine under that particular condition. During cold engine starts (engine speed below 200 RPM), M/C solenoid is turned off by ECM to provide rich mixture. Operating conditions which cause ECM to ignore oxygen sensor signals, causes the C-4 system to operate in open loop mode.