Mitsubishi Eclipse Technical Information Manual page 64

Operation
The Power-train Control Module (PCM) varies the
pulse width of the fuel injectors to provide precise
control of the air/fuel mixture. Wider pulse widths
increase the volume of fuel delivered to the cylinders.
The PCM uses the input from a number of sensors
in its attempt to reach and maintain this air/fuel
ratio. Manifold Absolute Pressure (MAP), and the
over injector pulse width. Other inputs such as the
Throttle Position Sensor (TPS), engine RPM, Engine
Exhaust gas
If a large amount of oxygen remains following the
combustion process, this sensor produces a low
voltage. This indicates a lean condition caused by
a ratio greater than stoichiometric. Little oxygen
in the exhaust allows the sensor to produce a higher
voltage, indicating a rich condition where the air/fuel
ratio is less than stoich.
ENGINE <NON-TURBO>
Upstream
sensor
- Control System
Coolant Temperature (ECT) Sensor, Intake Air Tem-
perature (IAT) Sensor. Vehicle Speed Sensor (VSS)
and battery voltage all have varying levels of influ-
ence on pulse width, depending on the circum-
stances.
As noted earlier, the system uses two oxygen sen-
sors both of which monitor the oxygen content of
the combustion byproducts on their way out of the
engine as exhaust. Only the upstream sensor has
authority over fuel injector pulse width.
Downstream 02
sensor
Upstream 02 sensor feedback to the PCM is used
to fine tune injector pulse width to maintain stoichio-
metric and meet emission standards. It can increase
or decrease injector pulse width by as much as
50%. Pulse width is calculated from the data sup-
plied from the MAP, TPS, ECT, IAT, upstream 02
sensor, battery voltage, RPM and VSS.
I-43