Signs and Symptoms of a Failing Ignition Coil in Vehicles

Signs and Symptoms of a Failing Ignition Coil in Vehicles

Have you ever experienced your car's engine misfiring or lacking power? These issues might signal a failing ignition coil. An ignition coil is a crucial component of your vehicle's ignition system, transforming low voltage into high voltage to spark the spark plugs, igniting the fuel and creating the power that propels your car.

CLEAR SIGNS OF A BAD IGNITION COIL

One clear sign of a bad ignition coil is a continuous fouling of spark plugs. If your spark plugs are continually fouled, there's a high likelihood that one or more of your ignition coils is failing. Additionally, an air leak can also cause similar symptoms, making it crucial to rule out other potential issues.

Due to my extensive knowledge, I recall a personal experience from over 20 years ago, where the primary coil resistance was measured at 11 ohms, significantly off the normal range of 0.9 ohms. In another instance, the secondary resistance between the cylinders of a car's ignition coil was recorded as infinity ohms, rather than the expected 6000 ohms, leading to a lack of power and engine performance issues. These symptoms are tell-tale signs that warrant further inspection and repair.

DIAGNOSTIC METHODS FOR IDENTIFYING A BAD IGNITION COIL

One of the easiest ways to diagnose a failing ignition coil without any diagnostic tools is to unplug the coils one by one while the vehicle is running. If the idle becomes worse after unplugging a particular coil, it suggests that coil is still in good working condition. However, when the faulty coil is unplugged, the idle should remain stable.

In computer-controlled engines, the most frequent reason for ignition coils to go bad is worn-out spark plugs. As the plug gap widens with wear and tear, it becomes harder for the spark to fire. The computer tries to compensate up to a certain point by increasing the ignition coil's duty cycle. Over time, the coil is forced to work harder than its design, leading to potential damage, such as cracking or even partial melting. This damage is often visible when you inspect the ignition coil.

Sometimes, the internal wires of the ignition coil can break or come loose, making visual inspection difficult. However, such issues can be detected using a multimeter. In such cases, diagnostic steps should be taken to switch the coils around and observe whether the misfires follow the coil or stay with a specific cylinder. If the misfires stay with a particular cylinder, the problem could be with either the spark plugs or the ECU (Engine Control Unit).

A historical note: In 2005, Ford faced an ECU design issue with coils, where certain coils could misfire through the ECU driver circuit. Fortunately, this driver circuit can be repaired or replaced by a mail-order vendor, mainly for V6 engines during that period.