Engine Control Module: Description and Operation
MODES OF OPERATIONAs input signals to the SBEC II change, the SBEC II adjusts the responses sent to the output devices. For example, the SBEC II must calculate a different injector pulse width and ignition timing for idle than it does for Wide Open Throttle (WOT). There are seven modes of operation that determine how the SBEC II 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 SBEC II receives input signals and responds only to preset SBEC II programming. Input from the oxygen (02) sensor is not monitored during OPEN LOOP modes. During CLOSED LOOP modes the SBEC II monitors the oxygen sensor input. This input indicates to the SBEC II 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 SBEC II can "fine tune" the injector pulse width to achieve optimum fuel economy and performance combined with low emission levels. The TBI system has the following modes of operation:
^ Ignition switch ON
^ Engine start-up (crank)
^ Engine warm-up
^ Idle
^ Cruise
^ Acceleration
^ Deceleration
^ Wide Open Throttle (WOT)
^ Ignition switch OFF
The ignition switch on, engine start-up (crank), engine warm-up, acceleration, deceleration, wide open throttle, and ignition switch OFF modes are OPEN LOOP modes. The idle and cruise modes, with the engine at operating temperature, are CLOSED LOOP modes.
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 II 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 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.
^ 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.
CRUISE
When the engine is at normal operating temperature, this is a CLOSED LOOP mode. When the engine is at cruising speed, 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
^ 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 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.
^ 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 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.
ACCELERATION
This is an OPEN LOOP mode. When the engine controller receives a sudden increase in throttle position or MAP pressure, it recognizes it as a demand for increased engine output. The engine controller responds by increasing injector pulse width to supply the necessary fuel for acceleration.
DECELERATION
When the engine is at normal operating temperature, this is a CLOSED LOOP mode. When the engine is under hard deceleration, 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)
^ Sync signal
^ Throttle Position Sensor (TPS)
If the engine controller receives a closed throttle input from the TPS and a sudden decrease in manifold pressure from the MAP sensor, it determines that hard deceleration is occurring. The engine controller will go into a fuel cut-off strategy, where it will remove the voltage from the injectors so that they cannot fire. The engine controller also ENERGIZES the EGR solenoid and the evaporative purge solenoid to prevent EGR flow and canister purge from occuring.
Based on the previous input signals, the following occurs:
^ 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 will send output signals to the Automatic Idle Speed (AIS) motor, to keep the idle speed within its rpm parameter.
^ If the engine controller receives inputs that indicate that the vehicle is under deceleration (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) until the vehicle is no longer decelerating.
WIDE OPEN THROTTLE
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.