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Home › GMC › 1983 › Forward Control 7.4 W, Standard › Repair and Diagnosis › Engine Performance › Ignition System - HEI › Overhaul › Reassembly › 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.