I-22
ENGINE <NON-TURBO>
-
Control System
-Upstream
The input from the upstream heated oxygen sensor
tells the PCM the oxygen content of the exhaust
gas. Based on this input, the PCM fine tunes the
air-fuel ratio by adjusting injector pulse width.
The sensor produces from 0 to 1 volt, depending
upon the oxygen content of the exhaust gas in the
exhaust manifold. When a large amount of oxygen
is present (caused by a lean air-fuel mixture), the
sensor produces voltage as low as 0.1 volt. When
there is a lesser amount of oxygen present (rich
air-fuel mixture) the sensor produces a voltage as
high as 1.0 volt. By monitoring the oxygen content
and converting it to electrical voltage, the sensor
acts as a rich-lean switch.
The heating element in the sensor maintains correct
oxygen sensor temperature. Maintaining correct
sensor temperature at all times allows the system
to enter into Closed Loop operation sooner. Also,
it allows the system to remain in Closed Loop opera-
tion during periods extended’ idle.
In Closed Loop operation the PCM monitors the
inputs from the heated oxygen sensors (along with
other inputs). In Closed Loop, the PCM adjusts injec-
tor pulse width based on the upstream heated oxy-
gen sensor input. During Open Loop operation the
PCM ignores the inputs from both the upstream
and downstream heated oxygen sensors. In Open
Loop, the PCM adjusts injector pulse width based
on preprogrammed (fixed) values and inputs from
other sensors.
The upstream oxygen sensor threads into the outlet
flange of the exhaust manifold.
Downstream
The downstream heated oxygen sensor threads
into the exhaust pipe at the rear of the catalytic
convertor. The downstream heated oxygen sensor
input is used to detect catalytic convertor
deteriora-
tion. As the convertor deteriorates, the input from
the downstream sensor begins to match the
up-
stream sensor input except for a slight time delay.
By comparing the downstream heated oxygen
sen-
sor input to the input from the upstream sensor,
the PCM calculates catalytic convertor efficiency.
_
Downstream heated
=
oxygen sensor
2
convertor
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