Article: The test above isn't the only way to determine whether the ignition coil in your vehicle is functioning as it should. If you have access to a piece of electrical equipment called an ohmmeter, which measures electrical resistance, you can measure the effectiveness of your ignition coil in a definitive, quantifiable way, rather than in the somewhat subjective way described above. However, to begin this test, you'll need to remove the vehicle's ignition coil so that you can easily access its electrical terminals. Refer to your service manual for precise instructions on removing your ignition coil. Usually, you'll need to disconnect it from the distributor wire, then unscrew it from its mounting with a wrench. Ensure your vehicle is turned off and has had a chance to cool before beginning this process. Every vehicle's ignition coil has its own unique specifications in terms of the electrical resistance within the coil. If your coil's actual resistance levels fall outside of these specifications, you'll know that your coil is damaged. Usually, you'll be able to find the resistance specifications unique to your vehicle by consulting your service manual. However, if you can't find it here, you may find success by contacting your dealership or by searching online vehicular resources. Generally speaking, most automotive coils will have a resistance reading of about .7 - 1.7 ohms for the primary winding and 7,500 - 10,500 ohms for the secondary winding. The distributor will have three electrical contacts - two on either side and one in the middle. These may be either external (jutting out) or internal (sunken in) - it makes no difference. Turn on your ohmmeter and touch one lead to each of the outer electrical contacts. Record the resistance reading - this is the resistance of the coil's primary winding. Note that some newer models of ignition coil have contact configurations that differ from this traditional arrangement. Consult your vehicle's manual for information if you are unsure which contacts correspond to the primary winding. Next, keep one lead on one of the outer contacts and touch the other to the central, inner contact of the ignition coil (where the main wire to the distributor connects). Record the resistance reading - this is the resistance of the coil's secondary winding. Ignition coils are delicate components of a vehicle's electrical system. If either the primary or secondary windings are even a little outside of your vehicle's specifications, you'll want to replace your ignition coil, as your current one is likely damaged or malfunctioning.
What is a summary of what this article is about?
Remove the ignition coil from the vehicle. Find the resistance specifications for your ignition coil. Position the leads of the ohmmeter on the poles of the primary coil. Position the leads of the ohmmeter on the poles of the secondary coil. Determine whether the readings you recorded fall within your vehicle's specifications.