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Ignition System Check

NOTE: Before making the following tests, secure an ignition spark tester. If tachometer is connected to ignition coil "TACH" terminal, disconnect it before performing tests. Use a digital voltmeter with 10 megohms impedance or larger.
  1. Remove spark plug wire and attach spark tester to wire. Crank engine and check for spark at tester gap. If there is no spark, check a second wire in same manner. If sparks result, ignition system is not at fault. Suspect fuel system or spark plugs.
  2. If no spark resulted in step 1), attach ignition tester to ignition coil secondary wire. Crank engine and recheck for spark at tester cap. If spark occurs, inspect distributor cap for water, cracks, or carbon tracking. If cap is OK, replace rotor.
  3. If no spark occurred in either step 1) or 2), remove distributor cap. Turn ignition system "ON". Check voltage at battery feed terminal (+) of HEI-EST module. Attach positive voltmeter lead to "+" terminal and negative lead to ground. Check for voltage while cranking engine.
  4. If reading is less than 10 volts, repair primary circuit back to ignition switch. If 10 volts or more, turn ignition "ON". Move positive voltmeter lead from HEI-EST "+" terminal to module "C" terminal. Leave negative lead grounded.
  5. If reading is under 1 volt, problem lies with open wire to ignition coil negative terminal, ignition coil connection or primary circuit of ignition coil. Repair or replace as necessary. If 10 volts or more is registered on voltmeter, proceed to step 7).
  6. If voltage reading on "C" terminal was 1-10 volts, replace distributor HEI-EST module and check for spark, following procedure outlined in steps 7) through 10). However, if a spark results in step 10), ignition system is OK following module replacement. If there is still no spark, replace ignition coil also, as it too is defective.
  7. If in step 5), 10 volts or more were read on module "C" terminal, remove pick-up coil connector from module. Turn ignition "ON". Check voltage again at module "C" terminal. Watch voltmeter as a test light is momentarily (not more than 5 seconds) connected to battery positive terminal to module "P" terminal.
  8. If no drop in voltage occurs, check HEI-EST module ground. Also check for open in wires from distributor cap (coil) to distributor. If OK, replace HEI-EST module.
  9. If voltage dropped, check for spark at tester gap (still attached to coil secondary terminal) when test light is removed from module "P" terminal. If spark occurs, either pick-up coil or its connections are defective.
    NOTE: Perform Distributor Pick-Up Coil Short and Resistance Check if not done previously. Resistance should be 500-1500 ohms.
  10. If no spark occurs and distributor module tester is available, check HEI-EST module. If OK, check ignition coil ground and coil-to-distributor wiring. If OK, replace ignition coil. If module is defective, replace.
  11. If no module tester is available, replace HEI-EST module and repeat step 9). If spark results, system is OK. If no spark results, original module is OK. Reinstall module and replace coil.
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