How to Troubleshoot a HEI Coil
High-energy ignition (HEI) systems replaced older systems that relied on breaker points and condensers for igniting the vehicle’s fuel-air mixture. In a HEI system, a high-voltage current runs through the ignition coil and is subsequently directed to the spark plugs for fuel-air ignition. If the vehicle develops bad fuel economy, rough idle or the engine starts missing under load or acceleration, the HEI coil may be one of the components responsible and may need to be replaced.
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Instructions
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Carbureted Engines
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1
Remove the distributor cap and set the ohmmeter to the “High” scale. Place one lead onto the positive terminal inside the distributor cap while keeping the other lead grounded on a metal surface. The resistance reading should display less than one ohm. Replace the coil if the reading displays more than one ohm.
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2
Place one lead onto the positive terminal inside the distributor cap while placing the other lead onto the rotor button. The resistance reading should display between 6,000 and 30,000 ohms. Replace the coil if the readings show infinity.
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3
Place the lead that was on the positive terminal onto the ground terminal. Maintain contact between the other lead and the rotor button. The resistance reading should display between 6,000 and 30,000 ohms.
Fuel Injected Engines
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4
Disconnect the distributor lead and wiring from the HEI coil. Set the ohmmeter to the “High” scale.
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5
Place one lead onto the positive terminal on the coil’s harness. Place the other lead onto the negative terminal on the coil’s harness. The resistance reading should display less than 1.20 ohms. Replace the coil if the readings show more than 1.20 ohms.
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6
Place one lead onto the positive terminal on the coil’s harness. Probe the high voltage cable terminal on the coil with the other lead. The resistance reading should display between 11,300 and 15,000 ohms. Replace the coil if the readings show a numeric value beyond these parameters.
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7
Maintain the lead connection on the positive terminal. Place the other lead onto the coil case. The resistance reading should display infinite resistance.
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1
Tips & Warnings
HEI coils manufactured by different companies may have different resistance ratings. Consult your vehicle’s repair manual or contact an automotive technician for more information.
