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Home >> Dodge or Ram Truck >> 1991 >> W 150 Pickup V8-360 5.9L >> Repair and Diagnosis >> Powertrain Management >> Computers and Control Systems >> Relays and Modules - Computers and Control Systems >> Engine Control Module >> Description and Operation

Engine Control Module: Description and Operation

MODES OF OPERATION

As input signals to the engine controller change, the engine controller adjusts the responses sent to the output devices. For example, the engine controller must calculate a different injector pulse width and ignition timing for idle than it does for Wide Open Throttle (WOT). There are eight modes of operation that determine how the engine controller 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 engine controller receives input signals and responds only to preset engine controller programming. Input from the oxygen (02) sensor is not monitored during OPEN LOOP modes. During CLOSED LOOP modes the engine controller monitors the oxygen sensor input. This input indicates to the engine controller 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 engine controller can "fine tune" the injector pulse width to achieve optimum fuel economy and performance combined with low emission levels. The Dual Point Fuel Injection (DPFI) system has the following modes of operation:

- Ignition switch ON
- Engine start-up (Crank)
- Engine warm-up
- Cruise
- Acceleration
- Deceleration
- Wide Open Throttle (WOT)
- Ignition switch OFF

The ignition switch ON, engine start-up (CRANK), engine warm-up, wide open throttle, ignition switch OFF, acceleration, and deceleration modes are OPEN LOOP modes. The cruise mode, with the engine at operating temperature, is a CLOSED LOOP mode.



IGNITION SWITCH ON

This is an OPEN LOOP mode. When the DPFI system is ACTIVATED by the ignition switch, the following actions occur:

- The engine controller reads atmospheric air pressure from the Manifold Absolute Pressure (MAP) sensor and calculates the basic fuel strategy.
- The engine controller monitors the coolant temperature sensor input, and uses this input to modify fuel strategy.
When the key is turned to the ON position (engine not running), the Auto ShutDown (ASD) relay is ACTIVATED for approximately 2 seconds, and if no distributor 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, fuel pump, injector, or oxygen sensor heater.

ENGINE START-UP

This is an OPEN LOOP mode. The following actions occur when the starter motor is engaged:

- If the engine controller receives an engine rotation signal from the Hall effect switch in the distributor it will ENERGIZE the Auto ShutDown (ASD) relay. The auto shutdown relay supplies voltage to the fuel pump, fuel injector, ignition coil, and oxygen sensor heater with battery voltage. If the engine controller does not receive an engine rotation signal from the Hall effect switch, the ASD relay will not be ENERGIZED.

- When the engine is operating normally and idling within +/-64 rpm of its specified rpm, the engine controller will compare the current MAP value with the atmospheric pressure reading it received during KEY-ON MODE. If a substantial difference is not detected between the two readings, then a pneumatic fault code is set in memory.

Once the ASD relay is ENERGIZED, the engine controller:
- Will supply the injectors with a ground path, firing them 8 times per engine revolution, instead of the usual 4 times per revolution.
- Will monitor coolant temperature, throttle body temperature, and barometric pressure (MAP sensor), at engine CRANKING only, to calculate the injector pulse width.
- Will monitor coolant temperature, distributor pick-up signal, MAP sensor, and throttle position. The engine controller uses these inputs to calculate the correct ignition timing.


ENGINE WARM-UP

This is an OPEN LOOP mode. The engine controller receives inputs from:

- Air conditioning switch
- Battery voltage
- Coolant temperature sensor
- Engine speed (distributor signal)
- Idle contact switch
- Manifold Absolute Pressure (MAP) sensor
- Neutral safety switch
- Throttle Body Temperature sensor
- Throttle Position Sensor (TPS)

The fuel injectors are controlled by the engine controller (switching the ground path), and it fires the injectors three times per engine revolution. The engine controller controls the idle speed, ignition timing, and throttle stop angle. For vehicles with a manual transmission, the up-shift indicator lamp is controlled by the engine controller based on engine load and speed.



CRUISE

This is a CLOSED LOOP mode, when the engine is at normal operating temperature. At cruising speed the engine controller receives inputs from:

- Air conditioning control positions
- Brake switch
- Coolant temperature sensor
- Engine speed sensor (distributor pick-up)
- Manifold Absolute Pressure (MAP) sensor
- Neutral safety switch (automatic transmission)
- Oxygen sensor
- Speed Control
- Throttle Position Sensor (TPS)
- Vehicle Distance (Speed) Sensor

Based on these inputs the following occurs:

- The engine controller controls the ground path to the fuel injectors by applying and removing the ground from their circuit. The length of time the ground is applied determines the injector pulse width. The engine controller also controls the sequence and times of injection per revolution. The engine controller also controls the engine idle speed, throttle stop angle, and ignition timing.
- The engine controller monitors the oxygen sensor input and adjusts air/fuel ratio, adjusts engine idle speed, and controls ignition timing. The engine controller adjusts the air/fuel ratio by controlling the injector pulse width, adjusts the engine idle speed by controlling the idle speed actuation motor, and adjusts the ignition timing through the ignition control module. For vehicles with a manual transmission, the up-shift indicator lamp is controlled by the engine controller based on engine load and speed.


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

This is a CLOSED LOOP mode. During deceleration the engine controller receives inputs from:

- Air conditioning control positions
- Coolant temperature sensor
- Engine speed (distributor pick-up)
- Idle contact switch
- Manifold Absolute Pressure (MAP) sensor
- Neutral safety switch
- Oxygen sensor
- 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 may reduce injector firing to once per engine revolution to maintain better control of the air fuel mixture. The engine controller also ENERGIZES the EGR solenoid and the evaporative purge solenoid to prevent EGR flow and canister purge from occuring. The engine controller may also ENERGIZE the air switching solenoid for short periods of time in response to a high vacuum signal sent to the engine controller by the MAP sensor.


WIDE OPEN THROTTLE

This is an OPEN LOOP mode. During wide open throttle operation the engine controller receives the following inputs:

- A/C switch
- Coolant temperature sensor
- Manifold Absolute Pressure (MAP) sensor
- Engine speed (distributor pick-up)
- Overdrive override switch
- Throttle Position Sensor (TPS)

During wide open throttle conditions the following occurs:

- 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 ENERGIZES the EGR solenoid and the canister purge solenoid to restrict EGR and purge system operation. The engine controller will also disengage the A/C compressor clutch through the clutch relay if the A/C select switch is ON.

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) Relay. When the ASD relay is 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.
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