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Home >> GMC >> 1987 >> Forward Control 4.8 T, Standard >> Repair and Diagnosis >> Engine Performance >> Ignition System >> Ignition System - HEI-Est (TBI Models) >> Testing >> Ignition Coil Resistance Check >> Primary Resistance
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Primary Resistance

  1. Set ohmmeter on high scale, attach leads as shown in step one. See Fig 1. Reading should be infinity. If not, replace coil.
  2. Remove coil connector. Using low scale, connect ohmmeter leads as shown in Step 2. Resistance should be zero or nearly zero. If not, replace ignition coil.
  3. With ohmmeter set on high range, connect leads as shown in step 2. See Fig 1. Meter should not read infinite (open circuit). If reading is infinite, replace coil.
Fig 1: Ignition Coil Resistance Test Points Remove all coil wires for testing. Courtesy of General Motors Corp.
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