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GMC
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1983
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Forward Control 7.4 W, Standard
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Repair and Diagnosis
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Engine Performance
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Ignition System - HEI
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Overhaul
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Reassembly
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Reading Scope Primary Pattern:
Reading Scope Primary Pattern:
A) Spark Zone
- spark plug arcing.
B) Coil & Condenser Zone
B1) Firing Zone
- no plug arc.
C) Dwell Zone
- displays current through coil primary with module turned on.