Monaco V6-182 3.0L SOHC (1990)
Engine Control Module: Description and Operation
MODES OF OPERATION
As input signals to the Engine Control Unit (ECU) change, the ECU adjusts its response that it sends to the output devices. For example, the ECU 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 ECU 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 ECU receives input signals and responds only to preset ECU
programming. Input from the oxygen (02) sensor is not monitored during OPEN LOOP modes. During CLOSED LOOP modes the ECU monitors the
oxygen sensor input. This input indicates to the ECU 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 ECU can "fine tune" the injector pulse width to achieve
optimum fuel economy and performance combined with low emission levels.
The Multi-Point Fuel Injection (MPFI) system has the following modes of operation:
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Ignition switch ON
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Engine start-up (CRANK)
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Engine warm-up
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Idle
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Cruise
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Deceleration
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Wide Open Throttle (WOT)
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Ignition switch OFF
The ignition switch ON, engine start-up (CRANK), engine warm-up, 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:
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The system power relay is ENERGIZED for one to three seconds.
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The ECU stores a barometric pressure value, preparing for engine start-up.
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The ECU OPENS the Idle Speed Regulator (ISR).
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The fuel pump is ACTIVATED by the ECU.
(The fuel pump will operate for approximately one to three seconds unless the engine is operating or the starter motor is engaged).
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The power latch relay is ENERGIZED for 1 to 3 seconds.
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The oxygen sensor heater element is ACTIVATED by the ignition relay.
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The EGR valve solenoid is ENERGIZED by the ECU preventing EGR valve operation.
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The injectors are ENERGIZED by the fuel pump relay, but no ground is established by the ECU.
The following engine sensors are ACTIVATED and begin providing input to the ECU:
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Coolant temperature sensor
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Manifold air temperature (MAT) sensor
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Manifold absolute pressure (MAP) sensor
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Throttle position sensor (TPS)
Battery voltage is also measured when the ignition switch is turned ON.
ENGINE START-UP
This is an OPEN LOOP mode. The following actions occur when the starter motor is engaged. The ECU receives inputs from:
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Battery voltage
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Coolant temperature sensor
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Manifold air temperature (MAT) sensor
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Manifold absolute pressure (MAP) sensor
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Starter motor relay
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Speed sensor
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Ignition switch
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Throttle position sensor (TPS)
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Injectors (voltage present at injector)
The fuel pump is ACTIVATED by the ECU. Voltage is applied to the fuel injectors with the ECU controlling the injection sequence and injector pulse
