Dakota 4WD V8-318 5.2L (1991)
Powertrain Control Module: Description and Operation
MODES OF OPERATION
As input signals to the engine controller change, the engine controller adjusts the responses sent to the output devices. For example, the engine
controller must calculate a different injector pulse width and ignition timing for idle than it does for Wide Open Throttle (WOT). There are eight modes
of operation that determine how the engine controller responds to the various input signals.
Modes of operation are separated into two different types, OPEN LOOP and CLOSED LOOP. During OPEN LOOP modes the engine controller
receives input signals and responds only to preset engine controller programming. Input from the oxygen (02) sensor is not monitored during OPEN
LOOP modes. During CLOSED LOOP modes the engine controller monitors the oxygen sensor input. This input indicates to the engine controller
whether or not the calculated injector pulse width results in the ideal air/fuel ratio of 14.7 parts of air to 1 part of fuel. By monitoring the exhaust oxygen
content, using the oxygen sensor, the engine controller can "fine tune" the injector pulse width to achieve optimum fuel economy and performance
combined with low emission levels. The Dual Point Fuel Injection (DPFI) system has the following modes of operation:
^
Ignition switch ON
^
Engine start-up (Crank)
^
Engine warm-up
^
Cruise
^
Acceleration
^
Deceleration
^
Wide Open Throttle (WOT)
^
Ignition switch OFF
The ignition switch ON, engine start-up (CRANK), engine warm-up, wide open throttle, ignition switch OFF, acceleration, and deceleration modes are
OPEN LOOP modes. The cruise mode, with the engine at operating temperature, is a CLOSED LOOP mode.
IGNITION SWITCH ON
This is an OPEN LOOP mode. When the DPFI system is ACTIVATED by the ignition switch, the following actions occur:
^
The engine controller reads atmospheric air pressure from the Manifold Absolute Pressure (MAP) sensor and calculates the basic fuel
strategy.
^
The engine controller monitors the coolant temperature sensor input, and uses this input to modify fuel strategy.
^
When the key is turned to the ON position (engine not running), the Auto ShutDown (ASD) relay is ACTIVATED for approximately 2
seconds, and if no distributor signal is received by the engine controller, the ground will be removed from the ASD circuit
DE-ACTIVATING the ASD relay. If the ASD relay is not ACTIVATED, battery voltage is not supplied to the ignition coil, fuel pump,
injector, or oxygen sensor heater.
ENGINE START-UP
This is an OPEN LOOP mode. The following actions occur when the starter motor is engaged:
^
If the engine controller receives an engine rotation signal from the Hall effect switch in the distributor it will ENERGIZE the Auto
ShutDown (ASD) relay. The auto shutdown relay supplies voltage to the fuel pump, fuel injector, ignition coil, and oxygen sensor
heater with battery voltage. If the engine controller does not receive an engine rotation signal from the Hall effect switch, the ASD relay
will not be ENERGIZED.
^
When the engine is operating normally and idling within +/-64 rpm of its specified rpm, the engine controller will compare the current
MAP value with the atmospheric pressure reading it received during KEY-ON MODE. If a substantial difference is not detected
between the two readings, then a pneumatic fault code is set in memory.
Once the ASD relay is ENERGIZED, the engine controller:
^
Will supply the injectors with a ground path, firing them 8 times per engine revolution, instead of the usual 4 times per revolution.
^
Will monitor coolant temperature and barometric pressure (MAP sensor), at engine CRANKING only, to calculate the injector pulse
width.
^
Will monitor coolant temperature, distributor pick-up signal, MAP sensor, and throttle position. The engine controller uses these inputs
to calculate the correct ignition timing.
ENGINE WARM-UP
This is an OPEN LOOP mode. The engine controller receives inputs from:
^
Air conditioning switch
^
Battery voltage
^
Coolant temperature sensor
