Cherokee 4WD L6-242 4.0L VIN S MFI (1992)
Engine Control Module: Description and Operation
Modes of Operation
Ignition Switch On
This is an OPEN LOOP mode. When the MPFI System is activated by the ignition switch, the following actions occur:
^
The Automatic Idle Speed (AIS) motor is pre-positioned by the engine controller for engine start-up.
^
The Manifold Absolute Pressure (MAP) sensor sends a signal to the engine controller, indicating the atmospheric pressure. The engine
controller uses this input to set the basic fuel strategy.
^
The Coolant Temperature Sensor sends a signal to the engine controller, indicating the current coolant temperature. The engine controller
uses this input to set the basic fuel strategy.
^
The Manifold Air Temperature (MAT) sensor and Throttle Position Sensor (TPS) inputs are monitored by the engine controller.
^
When the key is turned to the ON position (engine not running), the Auto Shutdown (ASD) relay is ACTIVATED for approximately 3
seconds, and if no crankshaft position 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 or the injectors.
^
The fuel pump is ACTIVATED by the fuel pump relay, via the ballast resistor, by the engine controller. The fuel pump will operate for
approximately 1 second, and if no crankshaft position signal or starter motor engagement signal is received by the engine controller, the
ground will be removed from the fuel pump relay circuit, DE-ACTIVATING the fuel pump. If the fuel pump relay is not ACTIVATED,
battery voltage is not supplied to the fuel pump or the oxygen sensor heating element.
^
The oxygen sensor heating element is ENERGIZED via the fuel pump relay, by the engine controller. It will remain ENERGIZED for
approximately 1 second, and if no crankshaft position signal or starter motor engagement signal is received by the engine controller, the
ground will be removed from the fuel pump relay circuit, DE-ENERGIZING the oxygen sensor heating element. If the fuel pump relay is not
ACTIVATED, battery voltage is not supplied to the fuel pump or the oxygen sensor heating element
^
The upshift indicator lamp is illuminated (Manual transmission).
Engine Start-Up
This is an OPEN LOOP mode. The following inputs are received by the SBEC when the starter motor is engaged:
^
Battery voltage
^
Coolant Temperature Sensor (CTS)
^
Crankshaft Position Sensor (CPS)
^
Manifold Air Temperature (MAT) sensor
^
Manifold Absolute Pressure (MAP) sensor
^
Starter motor relay
^
Sync signal
^
Throttle Position Sensor (TPS)
If the engine controller receives an engine rotation signal from the Crankshaft Position Sensor (CPS) it will ENERGIZE the Auto Shutdown (ASD
) and fuel pump relays. The auto shutdown relay supplies voltage to the fuel injectors and the ignition coil, and the fuel pump relay supplies
voltage to the fuel pump and the oxygen sensor heater element. If the engine controller does not receive an engine rotation signal from the
Crankshaft Position Sensor (CPS), within approximately 3 seconds of ignition switch ON signal, the fuel injection system will become
DE-ACTIVATED.
The fuel injector pulse width and injector firing sequence are controlled by the engine controller. The engine controller does this by switching the
ground to the injectors OFF and ON.
If the engine controller receives a wide open throttle signal from the Throttle Position Sensor (TPS), it assumes that a flooding condition exists and
it removes the ground from all of the injectors. Fuel injection will not occur until engine speed reaches at least 400 rpm.
The engine controller adjusts the ignition timing for different driving conditions based upon the input received from the Crankshaft Position
Sensor (CPS).
Engine Warm-Up
This is an OPEN LOOP mode. The following inputs are received by the SBEC:
^
Air conditioning select signal
^
Air conditioning request signal
^
Battery voltage
^
Coolant temperature sensor
^
Crankshaft Position Sensor (CPS)
