Fuel Control
All models equipped with ECC use feedback carburetors. Feedback carburetors use duty cycle solenoids to control air/fuel ratio. The air/fuel ratio is determined by the ECM in response to data sensor and vacuum switch signals.
The ECM monitors various engine operating conditions and calculates appropriate air/fuel ratio. The duty cycle ratio (time that solenoid is energized compared against time that solenoid is de-energized) is dependent upon coolant temperature, oxygen sensor signals, engine speed, engine load (intake manifold vacuum), and altitude.
When the ECM is changing air/fuel ratio based upon oxygen sensor information, the system is operating in closed loop mode. In closed loop, air/fuel ratio is dependent upon oxygen content of exhaust gases.
When coolant temperature and oxygen sensor temperature do not meet preset values, the system operates in open loop mode of operation. In open loop mode, the ECM issues air/fuel ratio commands to duty cycle solenoid based upon pre-programmed information.
Models equipped with Carter carburetors use 1 solenoid and models with Hitachi carburetors use 2 solenoids (slow and main circuits). The solenoid for Carter carburetors is an integral part of carburetor. The solenoids for Hitachi carburetors are externally mounted on intake manifold and are connected to the carburetor by air hoses. See Fig 2 .