Grand Cherokee 2WD L6-4.0L VIN S (1997)
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When engine has reached operating temperature, the PCM will begin monitoring 02S sensor input. The system will then leave the warm-up mode
and go into closed loop operation.
Idle Mode
IDLE MODE
When the engine is at operating temperature, this is a Closed Loop mode. At idle speed, the Powertrain Control Module (PCM) receives inputs from:
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Air conditioning select signal (if equipped)
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Air conditioning request signal (if equipped)
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Battery voltage
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Crankshaft Position (CKP) Sensor
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Engine Coolant Temperature (CTS) Sensor
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Intake Manifold Air Temperature (IAT) Sensor
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Manifold Absolute Pressure (MAP) Sensor
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Throttle Position Sensor (TPS)
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Camshaft Position Sensor (CPS)signal (in the distributor)
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Battery voltage
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Park/neutral switch (gear indicator signal-auto. trans. only)
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Oxygen (O2S) sensors
Based on these inputs, the following occurs:
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Voltage is applied to the fuel injectors with the Automatic Shutdown (ASD) relay via the PCM. The PCM will then control injection sequence and
injector pulse width by turning the ground circuit to each individual injector on and off.
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The PCM monitors the O2S sensor input and adjusts air-fuel ratio by varying injector pulse width. It also adjusts engine idle speed through the
Idle Air Control (IAC) motor.
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The PCM adjusts ignition timing by increasing and decreasing spark advance.
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The PCM operates the A/C compressor clutch through the clutch relay. This happens if A/C has been selected by the vehicle operator and
requested by the A/C thermostat.
Ignition Switch (Key-On) Mode
IGNITION SWITCH (KEY-ON) MODE
This is an Open Loop mode. When the fuel system is activated by the ignition switch, the following actions occur:
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The Powertrain Control Module (PCM) pre-positions the Idle Air Control (IAC) motor.
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The PCM determines atmospheric air pressure from the MAP sensor input to determine basic fuel strategy.
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The PCM monitors the engine coolant temperature sensor input. The PCM modifies fuel strategy based on this input.
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Intake manifold air temperature sensor input is monitored.
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Throttle Position Sensor (TPS) is monitored.
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The Auto Shutdown (ASD) relay is energized by the PCM for approximately three seconds.
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The fuel pump is energized through the fuel pump relay by the PCM. The fuel pump will operate for approximately three seconds unless the
engine is operating or the starter motor is engaged.
