How do I Test the Coil on the top of the distributor?

Discussion in 'General Chevy & GM Tech Questions' started by Holy Smoke, Jan 31, 2008.

  1. Holy Smoke

    Holy Smoke Rockstar 100 Posts

    Thanks for your help
    I suspect that the coil is bad. Electronic ign. I'm just wanting to learn if there is a test, with my multi-meter, to see if the coil is indeed bad. It probly is.
    There IS elec. to the dist. @ 12.2 volts. Batt. is long time without running. There is 12.2 at the top to the wire that goes into the coil pack on top. We also know that there is no spark.. Button, under cap, is new, rotor is new, cap new and wires new. The truck was running 2 weeks ago. Everything seemed fine. So this seems to be something that either works or doesn't work. Not somethings that weeeaarrrsss out.
    OR,, have I just done the coil test. hahaha:no: you tell me!!:sign0016: My spark has left me.:eek:h:
  2. 84fiero123

    84fiero123 Epic Member 5+ Years 1000 Posts Platinum Contributor

    I hate those type coils. It is so easy when you change the cap to put the wires in the wrong spots if you are not careful or have one to close to another and burn up the coil. Or just pinch one of the wires when you put the cover on the coil.

    All I have in the house at the moment is the manual for our 94 and it doesn’t cover the coil in the cap setup.

    Someone may know before I get to the shop for my other manual. If not, and I remember in the morning I will get the manual for the older trucks and post the test procedure.
  3. Holy Smoke

    Holy Smoke Rockstar 100 Posts

    Thanks much fiero. I want to make sure I'm not missing somethings else.... (gray matter)
  4. unplugged

    unplugged Epic Member 5+ Years 1000 Posts


    Ignition Coil
    See Figure 1
    1. Detach wiring connector from cap.
    2. Turn four latches using a screwdriver and remove cap and coil assembly from lower housing.
    3. Connect an ohmmeter between distributor cap terminals "TACH" and "BAT" to test the ignition coil's primary coil. The primary coil resistance should be less than 1.0 ohm (zero or nearly zero).
    4. Make the following ohmmeter measurements using a high resistance scale:
      1. Connect an ohmmeter between the carbon button in the cap and the "GRD" terminal on the distributor cap to test the ignition coil's secondary coil. Record your reading.
      2. Connect an ohmmeter between the carbon button in the cap and the "BAT" terminal on the distributor cap to test for short in the ignition coil. Record your reading.
      3. If infinite ohms or resistance was measured in both measurements, the ignition coil is defective and needs to be replaced.
    5. If the ignition coil tests OK, it's a good idea to test the pickup coil.
    Fig. 1: Checking coil resistance on the HEI system. Ohmmeter 1 shows the primary coil resistance connection. Ohmmeter 2 shows the secondary resistance connection. 1980 models shown, others similar

    These resistance checks will not disclose shorted coil windings. This condition can be detected only with scope analysis or a suitably designed coil tester. If these instruments are unavailable, replace the coil with a known good coil as a final coil test.

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