Spirit R/T L4-135 2.2L DOHC Turbo (1991)
Powertrain Control Module: Description and Operation
MODES OF OPERATION
As input signals to the engine controller change, the engine controller adjusts its response that it sends 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 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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Acceleration
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Deceleration
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Cruise
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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, wide open throttle, and ignition switch OFF modes are OPEN LOOP modes. The
acceleration, deceleration and cruise modes, with the engine at operating temperature, are CLOSED LOOP modes.
IGNITION SWITCH ON
This is an OPEN LOOP mode. When the Multi-Point Fuel Injection (MPFI) system is ACTIVATED by the ignition switch, the following actions occur:
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The engine controller reads atmospheric air pressure from the MAP sensor and calculates the basic fuel strategy.
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The engine controller monitors the throttle position sensor and engine coolant temperature sensor input. The engine controller uses
these inputs to modify fuel strategy.
When the key is turned to the ON position, the Auto ShutDown (ASD) relay is not ACTIVATED. For this reason, 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 crankshaft position sensor it will ENERGIZE the auto shutdown (ASD)
relay. The auto shutdown relay will supply 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 crankshaft position sensor, the ASD and fuel pump relays will not be
ENERGIZED.
Once the ASD and fuel pump relays are ENERGIZED, the engine controller:
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Will supply the injectors with a ground path, firing them just prior to intake valve opening.
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Will monitor coolant temperature, barometric pressure (at engine CRANKING only), and the number of engine revolutions since the
cranking was initiated. The engine controller uses these inputs to calculate the injector pulse width.
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Will monitor coolant temperature, crankshaft position, camshaft position, manifold absolute pressure, detonation sensor input, and
throttle position. The engine controller uses these inputs to calculate the correct ignition timing.
The following conditions must be met for the engine controller to set a pneumatic fault code into the memory:
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Engine running within 64 rpm of the desired rpm.
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Current operating rpm is greater than the START FUEL rpm.
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Vehicle is stationary.
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The difference between atmospheric pressure readings taken at start-up and current reading is not great enough.
ENGINE WARM-UP
This is an OPEN LOOP mode. The engine controller receives inputs from:
