Dakota 2WD V8-4.7L VIN J (2005)
Engine Control Module: Description and Operation
The PCM (1) is attached to the right-inner corner of the engine compartment.
MODES OF OPERATION
As input signals to the Powertrain Control Module (PCM) change, the PCM adjusts its response to the output devices.
The PCM will operate in two different modes: Open Loop and Closed Loop.
During Open Loop modes, the PCM receives input signals and responds only according to preset PCM programming. Input from the oxygen (O2S)
sensors is not monitored during Open Loop modes.
During Closed Loop modes, the PCM will monitor the oxygen (O2S) sensors input. This input indicates to the PCM whether or not the calculated
injector pulse width results in the ideal air-fuel ratio. This ratio is 14.7 parts air-to-1 part fuel. By monitoring the exhaust oxygen content through the
O2S sensor, the PCM can fine tune the injector pulse width. This is done to achieve optimum fuel economy combined with low emission engine
performance.
The fuel injection system has the following modes of operation:
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Ignition switch ON
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Engine start-up (crank)
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Engine warm-up
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Idle
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Cruise
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Acceleration
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Deceleration
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Wide open throttle (WOT)
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Ignition switch OFF
The ignition switch On, engine start-up (crank), engine warm-up, acceleration, deceleration and wide open throttle modes are Open Loop modes. The
idle and cruise modes, (with the engine at operating temperature) are Closed Loop modes.
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 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.
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The O2S sensor heater element is energized via the ASD relay. The O2S sensor input is not used by the PCM to calibrate air-fuel ratio during this
mode of operation.
