Cherokee 2WD L4-150 2.5L VIN P MFI (1991)
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 II:
^
Air conditioning select signal
^
Air conditioning request signal
^
Battery voltage
^
Coolant temperature sensor
^
Crankshaft Position Sensor (CPS)
^
Manifold Air/fuel Temperature (MAT) sensor
^
Manifold Absolute Pressure (MAP) sensor
^
Neutral safety switch (Automatic Transmission)
^
Sync signal
^
Throttle Position Sensor (TPS)
Based on the previous input signals, the following occurs:
^
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 adjusts the idle speed by controlling the Automatic Idle Speed (AIS) motor, and the ignition timing by controlling the
ignition module.
^
The engine controller controls the A/C compressor clutch via the A/C clutch relay, if the driver has selected A/C and if the A/C thermostat has
requested A/C.
^
The upshift indicator lamp is controlled by the engine controller (Manual Transmission).
^
Once the engine has reached normal operating temperature, the engine controller will monitor the Oxygen sensor's input. Once the engine
controller begins to monitor the Oxygen sensor's input, the engine controller leaves warm-up mode and enters closed loop operation.
IDLE
When the engine is at normal operating temperature, this is a CLOSED LOOP mode. When the engine is at idle, the controller receives the following
inputs:
^
Air conditioning select signal
^
Air conditioning request signal
^
Battery voltage
^
Coolant temperature sensor
^
Crankshaft Position Sensor (CPS)
^
Manifold Air/fuel Temperature (MAT) sensor
^
Manifold Absolute Pressure (MAP) sensor
^
Neutral safety switch (Automatic Transmission)
^
Oxygen sensor
^
Power steering high pressure switch
^
Sync signal
^
Throttle Position Sensor (TPS)
Based on the previous input signals, the following occurs:
^
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 signal from the power steering high pressure switch, it will increase the idle speed by adjusting the Automatic
Idle Speed (AIS) motor. This adjustment is made so that the engine does not die due to increased engine load.
^
The engine controller increases or decreases the ignition spark advance and ignition timing by applying and removing the ground path to the
ignition module.
^
The engine controller monitors the oxygen sensor's input, and changes the injector pulse width to keep the air/fuel ratio as close to 14.7:1 as
possible. As the injector pulse width is changing, the engine controller adjusts the Automatic Idle Speed (AIS) motor to keep the idle rpm at its
specified setting.
