How to Check the Resistance of a Motorcycle Ignition Coil

Written by chris gilliland Google
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Motorcycle engines rely on three different ingredients to create combustion: air, fuel and spark. If any of these factors are missing, combustion will not occur, leaving your motorcycle inoperable. Missing spark is a common issue, preventing the compressed air and fuel in the cylinder from being ignited. While the cause of a no-spark situation can vary, from improper ignition timing to a dead battery, a primary culprit is a faulty ignition coil, whose role is to transmit an electrical current to the spark plug. Testing a coil is simple enough using an ohmmeter; however, this process will only identify broken or badly shorted windings within the coil.

Skill level:
Moderate

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Things you need

  • Ohmmeter
  • Service manual (optional)

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Instructions

  1. 1

    Disconnect the ignition coil from the motorcycle's wiring harness and pull the spark plug caps from the spark plug. If possible, remove the entire coil from the motorcycle.

  2. 2

    Set your ohmmeter to the Rx1 range setting and place its positive lead (red) on the ignition coil's primary wire. The primary wire is connected to the motorcycle's breaker contacts (points) or CDI (Capacitor Discharge Ignition) box. Connect the negative lead (black) to a good ground location, such as the engine case or frame. Resistance should be very low, ranging between .5 to 1.5 ohms. If the resistance is higher than this range, the coil may be defective and will need replacement.

  3. 3

    Set your ohmmeter to the Rx100 range setting and place its positive lead (red) on the ignition coil's secondary wire. The secondary wire runs directly to the spark plug caps. Connect the negative lead (black) to a good ground location, such as the engine case or frame. Resistance should be very high, ranging between 6,000 to 13,000 ohms. If the resistance is lower than this range or does not indicate a reading, the coil may be defective and will need replacement.

  4. 4

    Install the ignition coil if it is within the specified ohm ranges. Replace the coil if it does not pass either of the two tests listed above.

Tips and warnings

  • Specific tools may be available from the manufacturer to test the ignition coil but may be cost-prohibitive. If you prefer to have the coil tested with these tools, contact your local dealership's service department to schedule an appointment.
  • Refer to the service manual specific to your motorcycle for detailed ignition coil removal instructions, testing procedures and specifications.
  • If you do not feel confident in your ability to complete this task, have the work completed by a qualified technician.
  • Use caution when working with your motorcycle's electrical system to prevent injury caused by electrical shock.

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