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Externally Mounted Ignition Coil

  1. Remove a spark plug wire and connect a spark tester to it. Check for spark while cranking engine. If no spark results, check for spark at another wire. If spark results, problem is in fuel system or spark plugs. If no spark occurs, proceed to step 2.
  2. If no spark occurred in step 1, remove the secondary ignition coil wire from the distributor cap. Connect spark tester to end of wire. Check for spark while cranking engine. If no spark occurs, proceed to step 3. If spark occurs, check distributor cap for water or cracks. If okay, replace rotor.
  3. Remove distributor cap but leave it connected to distributor with wiring harness. Connect negative voltmeter lead to ground and positive lead to HEI-EST module terminal "+". Turn ignition on. If voltage is 10 volts or more, proceed to step 4. If voltage is less than 10 volts, repair wire from terminal "+" to ignition coil and primary circuit to ignition switch.
  4. If voltage was 10 volts or more in step 3, leave ignition on and negative voltmeter lead grounded. Connect positive lead to HEI-EST module terminal "C". If voltage is under 1 volt, check for open or grounded lead from ignition coil to terminal "C", ignition coil connections or for an open primary circuit in ignition coil.
  5. If voltage was 10 volts or more, proceed to step 6. If voltage was 1-10 volts, replace HEI-EST module and check for spark from ignition coil as described in step 7. If sparks occur, system is operating properly. If no sparks occur, replace ignition coil as it too is defective.
  6. If voltage was 10 volts or more in step 4, remove pick-up coil connector from HEI-EST module. Connect negative voltmeter lead to ground and positive lead to HEI-EST module terminal "C". Turn ignition on. Momentarily connect a test light between battery voltage and HEI-EST module terminal "P" while observing voltmeter.
  7. If voltage does not drop, check HEI-EST module ground. If okay, replace HEI-EST module. If voltage does drop, use a spark tester and check for spark at end of coil wire as test light is removed from HEI-EST module terminal "P". If spark does not occur, proceed to step 8). If spark does occur, check pick-up coil and its connections. Also make sure pick-up coil is not grounded.
  8. If distributor module tester is available, check HEI-EST module. If okay, check secondary wire from distributor cap to ignition coil. If okay, replace ignition coil. If module is defective, replace. If no distributor module tester is available, replace the HEI-EST module and repeat step 7.
  9. If spark occurs, system is operating properly. If no spark occurs, HEI-EST module removed is okay. Reinstall original module and check secondary wire from distributor cap to ignition coil. If okay, replace ignition coil.
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