Cherokee 2WD L4-150 2.5L VIN P MFI (1991)
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The engine controller controls the A/C compressor clutch via the A/C clutch relay, if the driver has selected A/C and if the A/C thermostat has
requested A/C.
CRUISE
When the engine is at normal operating temperature, this is a CLOSED LOOP mode. When the engine is at cruising speed, the controller receives the
following inputs:
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Air conditioning select signal
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Air conditioning request signal
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Battery voltage
^
Coolant temperature sensor
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Crankshaft Position Sensor (CPS)
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Manifold Air/fuel Temperature (MAT) sensor
^
Manifold Absolute Pressure (MAP) sensor
^
Neutral safety switch (Automatic Transmission)
^
Oxygen sensor
^
Sync signal
^
Throttle Position Sensor (TPS)
Based on the previous input signals, the following occurs:
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The fuel injector pulse width and injector firing sequence are controlled by the engine controller. The engine controller does this by switching the
ground to the injectors OFF and ON.
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The engine controller monitors the oxygen sensor's input, and changes the injector pulse width to keep the air/fuel ratio as close to 14.7:1 as
possible.
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The engine controller increases or decreases the ignition spark advance and ignition timing by applying and removing the ground path to the
ignition module.
^
The engine controller controls the A/C compressor clutch via the A/C clutch relay, if the driver has selected A/C and if the A/C thermostat has
requested A/C.
ACCELERATION
This is an OPEN LOOP mode. When the engine controller receives a sudden increase in throttle position or MAP pressure, it recognizes it as a demand
for increased engine output. The engine controller responds by increasing injector pulse width to supply the necessary fuel for acceleration.
DECELERATION
When the engine is at normal operating temperature, this is a CLOSED LOOP mode. When the engine is under hard deceleration, the controller receives
the following inputs:
^
Air conditioning select signal
^
Air conditioning request signal
^
Battery voltage
^
Coolant temperature sensor
^
Crankshaft Position Sensor (CPS)
^
Manifold Air/fuel Temperature (MAT) sensor
^
Manifold Absolute Pressure (MAP) sensor
^
Neutral safety switch (Automatic Transmission)
^
Sync signal
^
Throttle Position Sensor (TPS)
If the engine controller receives a closed throttle input from the TPS and a sudden decrease in manifold pressure from the MAP sensor, it determines that
hard deceleration is occurring. The engine controller will go into a fuel cut-off strategy, where it will remove the voltage from the injectors so that they
cannot fire. The engine controller also ENERGIZES the EGR solenoid and the evaporative purge solenoid to prevent EGR flow and canister purge from
occuring.
Based on the previous input signals, the following occurs:
^
The engine controller increases or decreases the ignition spark advance and ignition timing by applying and removing the ground path to the
ignition module.
^
The engine controller will send output signals to the Automatic Idle Speed (AIS) motor, to keep the idle speed within its rpm parameter.
^
If the engine controller receives inputs that indicate that the vehicle is under deceleration (and the A/C has been selected by the driver), it will
DE-ENERGIZE the A/C clutch relay (DIS-ENGAGING the A/C compressor clutch) until the vehicle is no longer decelerating.
WIDE OPEN THROTTLE
