If you've noticed your vehicle's engine isn't running as smoothly as usual, it might be time to learn how to test a spark plug coil.

LRFIX also has a small engine resistance chart for checking your outdoor power equipment.

Safety First: Disconnect the Battery

Before you begin testing, prioritize safety. Disconnect the negative terminal of your car's battery to avoid any accidental electrical discharge during the process.

Locate the Spark Plug Coils

Spark Plug Coil Location

Identify the spark plug coils on your engine. Consult your car's manual for their specific location, usually connected to the spark plugs. Older vehicles use a single coil while newer vehicles use one coil, sometimes called a pencil coil, per cylinder.

Inspect for Physical Damage

Spar Plug Coils

Thoroughly examine the spark plug coils for any visible damage, such as cracks or burns. If you spot any, it's a clear indication that a replacement is necessary.

Use a Multimeter for Resistance Testing

Multimeter testing engine ignition coils

Employ a multimeter, setting it to the resistance or ohms setting. Disconnect the coil's electrical connector and measure the resistance across the primary and secondary terminals. Compare the readings with your vehicle's specifications.

Perform Continuity Testing: Ensuring a Complete Circuit

Continuity testing involves checking for a complete circuit within the coil.

A complete circuit ensures the smooth flow of electricity, playing a pivotal role in the ignition process.

To begin, set your multimeter to the continuity or beep setting. This setting allows you to identify if there is an uninterrupted path for the electrical current.

Once your multimeter is configured, disconnect the coil's electrical connector.

  • Primary Terminal Test:
    • Place one probe of the multimeter on the positive terminal of the primary side (where the electrical connector attaches) and the other on the negative terminal. The multimeter should indicate continuity, confirming that the primary circuit is intact.
  • Secondary Terminal Test:
    • Move on to the secondary side by placing one probe on the positive terminal (the high-tension lead where the spark plug wire connects) and the other on the negative terminal. Again, the multimeter should indicate continuity, ensuring an unbroken circuit in the secondary winding.
  • Complete Circuit Check:
    • With the probes still in place, check for continuity between the primary and secondary terminals. Any breaks in continuity during this test can indicate a fault in the coil. A healthy spark plug coil should provide uninterrupted electrical flow through both primary and secondary circuits.
  • Resistance Validation:
    • As continuity and resistance are interconnected, cross-verify the results with the resistance readings obtained in step 4. Consistency between the two tests reinforces the accuracy of your assessment.

Common Issues and Solutions

High ResistanceReplace the spark plug coil.
Low or No ContinuityInvestigate further or replace the coil.
Carbon TrackingReplace the spark plug coil.
Physical DamageReplace the spark plug coil.

By performing thorough continuity testing, you're not just ensuring that the circuit is complete; you're verifying that the coil can efficiently transfer electrical energy from the primary winding to the secondary winding.

This comprehensive evaluation minimizes the risk of overlooking potential issues, providing a more accurate picture of your spark plug coil's condition.

Conclusion and Opinion

Continuity testing is like the heartbeat check for your spark plug coil, it ensures a healthy flow of electricity, keeping your engine running smoothly.

A resilient spark plug coil, with a continuous beat of electricity, powers a car's heart with efficiency.