#### SYSTEM OPERATION

In operation, the on-board computer (control unit) calculates the basic injection pulse width by processing signals from the crank angle sensor and air flow meter. Receiving signals from each sensor which detects various engine operating conditions, the computer adds various enrichments (which are preprogrammed) to the basic injection amount. In this manner, the optimum amount of fuel is delivered through the injectors. The fuel is enriched when starting, during warm-up, when accelerating, when cylinder head temperature is high and when operating under a heavy load. The fuel is leaned during deceleration according to the closing rate of the throttle valve. Fuel shut-off is accomplished during deceleration, when vehicle speed exceeds 137 mph, or when engine speed exceeds 6400 rpm for about 500 revolutions.

The mixture ratio feedback system (closed loop control) is designed to control the air/fuel mixture precisely to the stoichiometric or optimum point so that the 3-way catalytic converter can minimize CO, HC and NOx emissions simultaneously. The optimum air/fuel fuel mixture is 14.7:1. This system uses an exhaust gas (oxygen) sensor located in the exhaust manifold to give an indication of whether the fuel mixture is richer or leaner than the stoichiometric point. The control unit adjusts the injection pulse width according to the sensor voltage so the mixture ratio will be within the narrow window around the stoichiometric fuel ratio. The system goes into closed loop as soon as the oxygen sensor heats up enough to register. The system will operate under open loop when starting the engine, when the engine temperature is cold, when exhaust gas sensor temperature is cold, when driving at high speeds or under heavy load, at idle (after mixture ratio learning is completed), during deceleration, if the e exhaust gas sensor malfunctions, or when the exhaust gas sensor monitors a rich condition for more than 10 seconds and during deceleration.

Ignition timing is controlled in response to engine operating conditions. The optimum ignition timing in each driving condition is preprogrammed in the computer. The signal from the control unit is transmitted to the power transistor and controls ignition timing. The idle speed is also controlled according to engine operating conditions, temperature and gear position. On manual transmission models, if battery voltage is less than 12 volts for a few seconds, a higher idle speed will be maintained by the control unit to improve charging function.

There is a fail-safe system built into the ECCS control unit. If the output voltage of the air flow meter is extremely low, the ECU will substitute a preprogrammed value for the air flow meter signal and allow the vehicle to be driven as long as the engine speed is kept below 2000 rpm. If the cylinder head temperature sensor circuit is open, the control unit clamps the warm-up enrichment at a certain amount. This amount is almost the same as that when the cylinder head temperature is between 68–176°F (20–80°C). If the fuel pump circuit malfunctions, the fuel pump relay comes on until the engine stops. This allows the fuel pump to receive power from the relay.