Ignition Coil Service Video

The ignition coil is a small transformer that converts 12-volt battery power into the high voltage needed to fire a spark plug. Most modern engines use one ignition coil per cylinder, mounted directly above each spark plug. This video shows what a coil-on-plug assembly looks like when removed from the valve cover and where cracks and carbon tracking can develop in the boot. It also explains how we identify the misfiring cylinder before replacing any parts.

Inside the ignition coil, the primary winding builds a magnetic field when the engine computer controls the ignition circuit. When that field collapses, it induces high voltage in the secondary winding, sending electricity through the boot and across the spark plug's electrode gap. When the coil windings, boot insulation, or connector deteriorates, the spark can weaken or fail, causing an engine misfire. The engine computer may detect the resulting change in crankshaft speed and store a cylinder-specific misfire code.

Drivers may notice a rough idle, a flashing check engine light during acceleration, or hesitation when merging onto I-55 or climbing the Kingshighway grade. These symptoms can become more noticeable under load because the engine requires more power. A persistent engine misfire often triggers a fault code that helps identify the affected cylinder. At Parks Automotive, we typically begin ignition coil inspections with check engine light diagnostics to pinpoint the problem.

At Parks Automotive, we review the freeze-frame data from the misfire code and move the suspected coil to another cylinder to see if the misfire follows it. We also inspect the spark plug and coil boot for oil intrusion or carbon tracking before recommending a replacement. Spark plugs and ignition coils can develop problems over time, so we may recommend replacing both if the plugs are nearing their service interval. We can often complete this work during the same visit as broader engine diagnostics, especially when the intake is already removed.

We use OE-equivalent ignition coils matched to the engine's ignition system. After installation, we clear the fault codes and road-test to confirm the misfire does not return.

Call Parks Automotive at (573) 335-2599 to have a suspected coil or misfire checked, or search online for  car repair near me in Cape Girardeau. Drivers from Jackson and Scott City bring vehicles here for the same work.