VIDEO: Diagnosing Ignition Related Misfires

Is the misfire the fault of the ignition coil, spark plug or could it be the spark plug wires. We’re going to find out how to test and rule out the wires. Sponsored by Blue Streak.

Ignition wires may not be as popular as a decade ago, but there are a lot of wires out there connecting spark plugs to coils and distributor caps.

Since they have to live under the hood, ignition wires are subjected to heat, oil and vibration. They can fail and cause a misfire and code.

Be sure to first visually inspect the wires and engine.

One of the most damaging elements under the hood is vibration. Excessive vibration can loosen the connection at the coil, plug or distributor cap. This can increase the resistance and energy required to fire the spark plug and damage the spark plug. Look at the general condition of the engine and check for issues like vacuum leaks and even excessive carbon deposits. Also, look at how the coils and wires are mounted to the engine.

Heat can burn wire insulation and boots. If the wire or boot is crispy it is more likely to offer the spark an easier path to ground. Look for missing heat shields and spark plug wires that were not properly routed past exhaust manifolds.

Look at the wire to see if there is any damage due to rubbing against other engine parts. Abrasions to the outside of the wire insulation can cause sparks to jump and impacts can crush and damage the wire inside insulation. Make sure to inspect the motor and transmission mounts for excessive movement.

Last, use an ohmmeter with the leads attached to both connectors of the spark plug wire. The resistance for most resistor core wire is between 10,000 to 12,000 ohms-per-foot. However, consult the service information for the correct value.

By performing these easy checks, you can determine if the spark plug wires are the problem or it is another component in the ignition system or on the engine.

Courtesy of Underhood Service.