Operation CHARM
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GMC Truck
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1989
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K 2500 Truck 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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Scan Tool Testing and Procedures
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Knock Retard
Knock Retard
On 1987-90 engines the display indicates the number of degrees the ECM is retarding the EST spark timing.