Grand Cherokee 2WD V8-4.7L VIN J (2004)
-
Acceleration
-
Deceleration
-
Wide open throttle (WOT)
-
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.
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:
-
The PCM pre-positions the idle air control (IAC) motor.
-
The PCM determines atmospheric air pressure from the MAP sensor input to determine basic fuel strategy
-
The PCM monitors the engine coolant temperature sensor input. The PCM modifies fuel strategy based on this input.
-
Intake manifold air temperature sensor input is monitored.
-
Throttle Position Sensor (TPS) is monitored.
-
The auto shutdown (ASD) relay is energized by the PCM for approximately three seconds.
-
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.
-
The O(2)S sensor heater element is energized via the O(2)S relays. The O(2)S sensor input is not used by the PCM to calibrate air-fuel ratio
during this mode of operation.
Engine Start-Up Mode
This is an Open Loop mode. The following actions occur when the starter motor is engaged.
The PCM receives inputs from:
-
Battery voltage
-
Engine coolant temperature sensor
-
Crankshaft position sensor
-
Intake manifold air temperature sensor
-
Manifold Absolute Pressure (MAP) sensor
-
Throttle position sensor (TPS)
-
Starter motor relay
-
Camshaft position sensor signal
The PCM monitors the crankshaft position sensor. If the PCM does not receive a crankshaft position sensor signal within approximately 3 seconds
of cranking the engine, it will shut down the fuel injection system.
The fuel pump is activated by the PCM through the fuel pump relay.
Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control the injection sequence and injector pulse width
by turning the ground circuit to each individual injector ON and OFF.
The PCM determines the proper ignition timing according to input received from the crankshaft position sensor.
Engine Warm-Up Mode
This is an Open Loop mode. During engine warmup, the PCM receives inputs from:
-
Battery voltage
-
Crankshaft position sensor
-
Engine coolant temperature sensor
-
Intake manifold air temperature sensor
-
Manifold absolute pressure (MAP) sensor
-
Throttle position sensor (TPS)
-
Camshaft position sensor signal
-
Park/neutral switch (gear indicator signal-auto. trans. only)
-
Air conditioning select signal (if equipped)
-
Air conditioning request signal (if equipped)
Based on these inputs the following occurs:
-
Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control the injection sequence and injector pulse
width by turning the ground circuit to each individual injector ON and OFF.
-
The PCM adjusts engine idle speed through the idle air control (IAC) motor and adjusts ignition timing.
-
The PCM operates the A/C compressor clutch through the clutch relay. This is done if A/C has been selected by the vehicle operator and
requested by the A/C thermostat.
-
When engine has reached operating temperature, the PCM will begin monitoring O(2)S sensor input. The system will then leave the warm-up
mode and go into closed loop operation.
