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Home >> GMC >> 1986 >> Forward Control 7.4 W, Automatic, 400/M40 >> Repair and Diagnosis >> Engine Performance >> Ignition System >> Ignition System - HEI (Federal) >> Overhaul >> Reading Scope Primary Pattern
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Reading Scope Primary Pattern

  1. Spark Zone - spark plug arcing.
  2. Coil and Condenser Zone.
  3. Dwell Zone - displays current through coil primary with module activated.
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