ENGINE AND EMISSION CONTROL SYSTEM DESCRIPTION — Fuel Injection Control (Cont'd)

EF & EC-15prose procedure

Mixture ratio feedback control and self-learning control sections apply to catalyzer (catalyst) model only.

Fuel Injection Control (Cont'd)

MIXTURE RATIO FEEDBACK CONTROL (For catalyzer model)

Mixture ratio feedback system is designed to precisely control the mixture ratio to the stoichiometric point so that the three-way catalyst can reduce CO, HC and NOx emissions. This system uses an exhaust gas sensor in the exhaust manifold to check the air-fuel ratio. The control unit adjusts the injection pulse width according to the sensor voltage so the mixture ratio will be within the range of the stoichiometric air-fuel ratio.

This stage refers to the closed-loop control condition. The open-loop control condition refers to that under which the E.C.U. detects any of the following conditions and feedback control stops in order to maintain stabilized fuel combustion.

Open-loop control conditions

1
Deceleration
2
High-load, high-speed operation
3
Engine idling
4
Malfunctioning of exhaust gas sensor or its circuit
5
Insufficient activation of exhaust gas sensor at low engine temperature
6
Engine starting

MIXTURE RATIO SELF-LEARNING CONTROL (For catalyzer model)

The air-fuel ratio feedback control system monitors the air-fuel signal transmitted from the exhaust gas sensor. This feedback signal is then sent to the E.C.U. to control the amount of fuel injection to provide a basic air-fuel ratio as close to the theoretical air-fuel ratio as possible. However, the basic air-fuel ratio is not necessarily controlled as originally designed. This is due to manufacturing errors (e.g., air flow meter hot wire) and changes during operation (injector clogging, etc.) of E.C.C.S. parts which directly affect the air-fuel ratio.

Accordingly, a difference between the basic and theoretical air-fuel ratios is quantitatively monitored in this system. It is then computed in terms of "fuel injection duration" to automatically compensate for the difference between the two ratios.

FUEL INJECTION TIMING

Fuel is injected once a cycle for each cylinder in the firing order.