Durango 2WD V8-5.9L VIN Z LDC (2000)
Powertrain Control Module: Description and Operation
PCM Operating Modes
PCM OPERATING MODES
As input signals to the PCM change, the PCM adjusts its response to output devices. For example, the PCM must calculate a different injector
pulse width and ignition timing for idle than it does for wide open throttle. There are several different modes of operation that determine how the
PCM responds to the various input signals.
There are two types of engine control operation: open loop and closed loop.
In open loop operation, the PCM receives input signals and responds according to preset programming. Inputs from the heated oxygen sensors are
not monitored.
In closed loop operation, the PCM monitors the inputs from the heated oxygen sensors. This input indicates to the PCM whether or not the
calculated injector pulse width results in the ideal air-fuel ratio of 14.7 parts air to 1 part fuel. By monitoring the exhaust oxygen content through
the oxygen sensor, the PCM can fine tune injector pulse width. Fine tuning injector pulse width allows the PCM to achieve optimum fuel economy
combined with low emissions.
The engine start-up (crank), engine warm-up, and wide open throttle modes are open loop modes. Under most operating conditions, the
acceleration, deceleration, and cruise modes, with the engine at operating temperature, are closed loop modes.
Ignition Switch ON (Engine OFF) Mode
When the ignition switch activates the fuel injection system, the following actions occur:
1. The PCM determines atmospheric air pressure from the MAP sensor input to determine basic fuel strategy.
2. The PCM monitors the engine coolant temperature sensor and throttle position sensor input. The PCM modifies fuel strategy based on this
input.
When the ignition key is in the "ON" position and the engine is not running (0 rpm), the auto shutdown relay and fuel pump relay are not
energized. Therefore, voltage is not supplied to the fuel pump, ignition coil, and fuel injectors.
Engine Start-up Mode
This is an open loop mode. The following actions occur when the starter motor is engaged:
1. The auto shutdown and fuel pump relays are energized. If the PCM does not receive the camshaft and crankshaft signal within approximately
one second, these relays are de-energized.
2. The PCM energizes all fuel injectors until it determines crankshaft position from the camshaft and crankshaft signals. The PCM determines
crankshaft position within one engine revolution. After the crankshaft position has been determined, the PCM energizes the fuel injectors in
sequence. The PCM adjusts the injector pulse width and synchronizes the fuel injectors by controlling the fuel injectors' ground paths.
Once the auto shutdown and fuel pump relays have been energized, the PCM determines the fuel injector pulse width based on the following:
-
engine coolant temperature
-
manifold absolute pressure
-
intake air temperature
-
engine revolutions
-
throttle position
The PCM determines the spark advance based on the following:
-
engine coolant temperature
-
crankshaft position
-
camshaft position
-
intake air temperature
-
manifold absolute pressure
-
throttle position
Engine Warm-Up Mode
This is an open loop mode. The PCM adjusts injector pulse width and controls injector synchronization by controlling the fuel injectors' ground
paths. The PCM adjusts ignition timing and engine idle speed. The PCM adjusts the idle speed by controlling the idle air control motor.
Cruise or Idle Mode
When the engine is at normal operating temperature, this is a closed loop mode. During certain idle conditions, the PCM may enter into a variable
idle speed strategy. At this time, the PCM adjusts engine speed based on the following inputs:
-
throttle position
-
battery voltage
-
engine coolant temperature
Acceleration Mode
