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Home >> Oldsmobile >> 1987 >> Custom Cruiser >> Repair and Diagnosis >> Engine Performance >> Ignition System - HEI-Est >> Testing >> Ignition System Check >> Externally Mounted Ignition Coil
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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 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, 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. If spark is present while cranking, and distributor cap is free from cracks or other defects replace rotor. If no spark occurred while cranking, remove distributor cap with ignition on and check voltage at HEI (EST) module terminal "+". If measurement is less than 10-volts, repair wire from terminal "+" to ignition coil as well as from primary circuit to ignition switch. If measurement is between 1 and 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 1 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 then proceed to step 8.
  8. Check HEI-EST module with Module Tester (J-26792). Replace module if defective. If module okay, check coil wire from distributor cap to ignition coil. If coil wire okay, replace ignition coil. If no Distributor Module Tester (J-26792) is available, check coil wire from distributor cap. If good, replace ignition coil and repeat step 6).
  9. If spark occurs, system is operating properly. If no spark occurs, original coil is good. Reinstall original coil and replace module.
NOTE: If tachometer is connected to ignition coil "TACH" terminal, disconnect it before performing tests. Use digital voltmeter with 10 megaohms or greater impedance.
CAUTION: When removing spark plug wire from spark plug, twist and pull on boot, NOT on wire.
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