General System Description

Modes of Operation
The two modes of air/fuel ratio solenoid control are;
- Open-Loop Control
- Closed-Loop Control
The mode of operation used at any time depends on; coolant temperature, engine rpm, throttle valve operation, charging system voltage, oxygen content of exhaust gas, gear position, clutch operation, or air/fuel ratio solenoid operation.

Open-Loop Control
The ECC control unit operates the air/fuel ratio solenoid in open-loop mode under the following conditions to improve driveability:
- Battery voltage is less than or equal to 10 volts.
- Engine speed is less than 400 rpm.
- Coolant temperature is less than 122° F.
- Oxygen sensor output voltage is less than 200-300 millivolts.
- During deceleration--when the fuel shut-off system is operating.
- When engine speed is greater than or equal to 3600 rpm (engine revolution switch off).

Closed-Loop Control
System functions in closed loop after the engine has warmed-up and the exhaust gas sensor has reached operating temperature.
- ECC control unit controls air/fuel ratio precisely at the stoichiometric point by adjusting the mixture control solenoid pulse width--according to exhaust gas sensor voltage--allowing the three way catalyst to minimize all exhaust emissions simultaneously.
- The nonlinear voltage from the exhaust gas sensor--located in the exhaust manifold--indicates whether the air/fuel mixture is leaner or richer than the stoichiometric point.