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Externally Mounted Ignition Coil

  1. Disconnect a spark plug wire and connect spark tester. Check for spark while cranking engine. If no spark is present, check for spark at any other wire. If spark still is not present, go to step 2). Intermittent sparking is considered no spark. If spark results, problem is in fuel system or spark plugs.
  2. Disconnect 4-terminal EST connector. Check for spark. If spark occurs, replace pick-up coil. If no spark occurs, check for spark at coil wire with Spark Tester (ST-125) while cranking engine.
    NOTE: Leave Spark Tester (ST-125) connected during remainder of tests.
  3. Ensure that spark is present while cranking. If distributor cap is free from cracks or other defects, replace rotor. If no spark occurred while cranking, remove distributor cap. Turn ignition on and check voltage at HEI (EST) module terminal "+". If measurement is less than 10 volts, repair wire from terminal "+" to ignition coil. Also check wire from primary circuit to ignition switch. If measurement is 1-10 volts, proceed to step 4). If voltage was more than 10 volts, proceed to step 5).
  4. Replace HEI (EST) module and check for spark at ignition coil. If spark occurs, system is operating properly. If no spark occurs, replace ignition coil.
  5. With ignition switch in "ON" position, check voltage at HEI (EST) module terminal "C". If voltage is less than one volt at terminal "C", check for open or grounded lead from ignition coil to terminal "C". If voltage is 10 volts or more, proceed to step 6). Also check ignition coil connections for an open primary circuit.
  6. Remove pick-up coil connector from HEI (EST) module. Check voltage at HEI (EST) module terminal "C" with ignition switch in "ON" position. Momentarily connect a test light between battery positive terminal 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 drops, use a spark tester and check for spark at end of coil wire as test light is removed from module terminal "P". If spark occurs, check pick-up coil and its connections. If spark does not occur, ensure pick-up coil is not grounded and proceed to step 8).
  8. Check HEI-EST module with Module Tester (J-26792). Replace module if defective. If module tests okay, check coil wire from distributor cap to ignition coil. If coil wire is okay, replace ignition coil. If no Distributor Module Tester (J-26792) is available, check coil wire from distributor cap. If okay, replace ignition coil and repeat step 6).
  9. If spark occurs, system is operating properly. If no spark occurs, original coil is okay. Reinstall original coil and replace module.
NOTE: If tachometer is connected to ignition coil "TACH" terminal, disconnect before performing tests. Use digital voltmeter with 10-megohms or greater impedance.
CAUTION: When removing spark plug wire from spark plug, twist and pull on boot, NOT on wire.
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