Operation CHARM
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GMC Truck
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1988
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V 3500 P/U 4WD V8-454 7.4L VIN N TBI
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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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Testing and Inspection
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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.