GM Full-Size Trucks 1970-1979 Repair Guide

Ignition Coil

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REMOVAL & INSTALLATION



  1. A 6-cylinder EST distributor with coil-in-cap is illustrated.
  2.  
  3. Detach wiring connector from cap, as shown.
  4.  
  5. Turn four latches and remove cap and coil assembly from lower housing.
  6.  
  7. Connect ohmmeter. Test 1.
  8.  
  9. Reading should be zero, or nearly zero. If not, replace coil. Step 8.
  10.  
  11. Connect ohmmeter both ways. Test 2. Use high scale. Replace coil only if both readings are infinite. Step 8.
  12.  
  13. If coil is good, go to Step 13.
  14.  
  15. Remove coil cover attaching screws and lift off cover.
  16.  
  17. Remove ignition coil attaching screws and lift coil with leads from cap.
  18.  
  19. Remove ignition coil arc seal.
  20.  
  21. Clean with soft cloth and inspect cap for defects. Replace, if needed.
  22.  
  23. Assemble new coil and cover to cap.
  24.  
  25. On all distributors, including distributors with Hall Effect Switch identified in Step 27, remove rotor and pickup coil leads from module.
  26.  
  27. Connect ohmmeter Test 1 and then Test 2.
  28.  
  29. If vacuum unit is used, connect vacuum source to vacuum unit. Replace unit if inoperative. Observe ohmmeter throughout vacuum range: flex leads by hand without vacuum to check for intermittent opens.
  30.  
  31. Test 1 should read infinite at all times. Test 2 should read steady at one value within 500-1,500 ohms range.
  32.  

Ohmmeter may deflect if operating vacuum unit causes teeth to align. This is not a defect.

  1. If pickup coil is defective, go to Step 18. If okay, go to Step 23.
  2.  
  3. Mark distributor shaft and gear so they can be reassembled in same position.
  4.  
  5. Drive out roll pin.
  6.  
  7. Remove gear and pull shaft assembly from distributor.
  8.  
  9. Remove three attaching screws and remove magnetic shield.
  10.  
  11. Remove retaining ring and remove pickup coil, magnet and pole piece.
  12.  
  13. Remove two module attaching screws, and capacitor attaching screw. Lift module, capacitor and harness assembly from base.
  14.  
  15. Disconnect wiring harness from module.
  16.  
  17. Check module with an approved module tester.
  18.  
  19. Install module, wiring harness, and capacitor assembly. Use silicone lubricant on housing under module.
  20.  
  21. The procedures previously covered, Steps 1-26, apply also to distributors with Hall Effect Switches.
  22.  

 
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