Operation CHARM
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GMC Truck
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1987
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V 3500 P/U 4WD V8-305 5.0L
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Repair and Diagnosis
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Powertrain Management
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Computers and Control Systems
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Relays and Modules - Computers and Control Systems
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Engine Control Module
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Description and Operation
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Modes of Operation
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Deceleration Mode
Deceleration Mode
In the Deceleration Mode, the ECM senses changes in throttle position and manifold pressure and reduces fuel delivery. When decelerating very rapidly, the ECM can cut off fuel completely for short periods of time.