Vacuum Switches
Two vacuum switches are used because the feedback system does not respond quickly enough to provide good driveability under full-load or cold operation. The vacuum switches are used to limit closed loop operation under these conditions.
When manifold vacuum is less than preset value, vacuum switch I signals the ECM to shut the duty cycle solenoid(s) off. Closed loop operation is also prevented by vacuum switch II, when the engine is warm and vacuum falls below a preset value (during acceleration/deceleration). After a lapse of about 5 seconds, the switch returns control of duty cycle solenoid(s) to ECM.