Mixture Control Solenoid - Slow Cut: Description and Operation

Solenoid Valve Locations:

This valve is located in the carburetor float chamber cover.

Solenoid Valve Duty Cycle:

The ECU controls the air-fuel ratio by controlling the duty cycle of the valve. The frequency of ON-OFF cycles remain constant at 10 Hz pulses, but the solenoid "ON" time portion of each cycle is changed to modify the duty ratio. The higher the duty ratio (the longer the ON time), the leaner the air-fuel ratio.

Slow Cut Solenoid Valve (SCSV):

The SCSV controls the amount of air allowed to bleed into the idle jet and transition port fuel feed passage. When the SCSV is de-energized, the slow fuel passage vent is closed, and the idle and transition circuits operate normally. When the SCSV is energized, the slow fuel vent passage is opened. This allows a much larger amount of air into the passage effectively shutting off the fuel flow. With the ON-OFF operation (duty cycle) of the SCSV, the air-fuel ratio is controlled.
For a more detailed description, and for ECU diagnostic procedures refer to COMPUTERIZED ENGINE CONTROLS.