Swift GL L4-1298cc 1.3L SOHC MFI (2000)
Air/fuel ratio feed back compensation (Closed loop system)
It is necessary to keep the air/fuel mixture close to the theoretical air/fuel ratio (14.7) to obtain efficient performance of the 3-way catalytic converter and
high clarification rate of CO, HC and NOx in the exhaust gas. For that purpose, ECM (PCM) operates as follows. It first compares the signal from the
heated oxygen sensor-1 with a specified reference voltage and if the signal is higher, it detects that the air/fuel ratio is richer than the theoretical air/fuel
ratio and reduces fuel. On the other hand, if the signal is lower, it detects that the air/fuel ratio is leaner and increases fuel. By repeating these operations,
it adjusts the air/fuel ratio closer to the theoretical air/fuel ratio.
1. When oxygen concentration in the exhaust gas is low, that is, when the air/fuel ratio is smaller than the theoretical air/fuel ratio (fuel is richer),
electromotive force of the heated oxygen sensor increases and a rich signal is sent to ECM (PCM).
2. Upon receipt of the rich signal, ECM (PCM) decreases the amount of fuel injection, which causes oxygen concentration in the exhaust gas to
increase and electromotive force of the heated oxygen sensor-1 to decrease. Then a lean signal is sent to ECM (PCM).
3. As ECM (PCM) increases the amount of fuel injection according to the lean signal, oxygen concentration in the exhaust gas decreases and the
situation is back to above 1)
This control process, however, will not take place under any of the following conditions.
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At engine start and when fuel injection is increased after engine start
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When engine coolant temperature is low
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When highly loaded and fuel injection is increased
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At fuel cut
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When heated oxygen sensor is cold
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When engine is running at high speed (higher than about 4000 r/min).
