How to Test a GM Ignition Coil

by Christian Killian
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Testing or checking an ignition coil can tell you a lot about the health of your ignition system. Since the coil is the center of the system, it has to be working right or the car will not run right. Testing the coil requires an ohms meter. If you do not have one, you can buy one at a home center or building center that carries electrical supplies. The procedure for testing the coil is the same for every ignition coil out there, but if your car has coil packs, it may require a different procedure.

Step 1

Remove the wires from the positive and negative terminals on the coil using a wrench to remove the nuts from the studs. Unplug the coil wire that runs from the coil high tension terminal to the distributor and lay it aside.

Step 2

Place one test lead from the ohms meter on the negative post and one on the positive post of the coil. it doesn't matter which lead goes on which post because you are measuring resistance, not amps or volts. The reading should be between .70 and 1.7 ohms. If it is outside that range, the coil is defective.

Step 3

Place a lead from the ohmmeter on either side terminal and one in the center high tension terminal. Read the ohms off the meter. You are looking for 7500 to 10,500 ohms, and if the reading falls outside that range, it indicates a defective coil.

Step 4

Reattach the wires to the positive and negative side terminals followed by the retaining nuts for both sides. Tighten the nuts with a wrench. Plug the coil wire back into the high tension terminal in the center of the coil. If the coil is outside the ranges here, do not reinstall it. Instead, replace the coil right away.

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