Cherokee 2WD L4-150 2.5L VIN P MFI (1991)
This is an OPEN LOOP mode. When the engine is experiencing a wide open throttle condition, the controller receives the following inputs:
^
Battery voltage
^
Coolant temperature sensor
^
Crankshaft Position Sensor (CPS)
^
Manifold Air/fuel Temperature (MAT) sensor
^
Manifold Absolute Pressure (MAP) sensor
^
Sync signal
^
Throttle Position Sensor (TPS)
Based on the previous input signals, the following occurs:
^
The fuel pump ballast resistor is bypassed, allowing full system voltage to be applied to the fuel pump via the ballast bypass relay.
^
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.
^
The engine controller ignores the oxygen sensor input signal and provides a predetermined amount of additional fuel by adjusting injector pulse
width.
^
The engine controller increases or decreases the ignition spark advance and ignition timing by applying and removing the ground path to the
ignition module.
^
If the engine controller receives inputs that indicate that the vehicle is experiencing a wide open throttle condition (and the A/C has been selected
by the driver), it will DE-ENERGIZE the A/C clutch relay (DIS-ENGAGING the A/C compressor clutch) for approximately 15 seconds or until
the vehicle is no longer experiencing a wide open throttle condition.
^
The upshift indicator lamp is controlled by the engine controller (Manual Transmission).
IGNITION SWITCH OFF
This is an OPEN LOOP mode. When the key is placed in the OFF position, the engine controller removes the ground from the Auto Shutdown (ASD)
and Fuel Pump relays. When the ASD and Fuel Pump relays are DE-ENERGIZED, no battery voltage is allowed to flow to the fuel pump, fuel injectors,
ignition coil, or oxygen sensor heating element. When this occurs, all fuel injection, and other systems controlled by the SBEC, cease to function.
