* Misfires: This is the most common symptom. A bad coil won't provide enough spark to one or more cylinders, leading to rough idling, sputtering, hesitation during acceleration, and a noticeable decrease in power. You might also hear a popping or backfiring sound from the exhaust.
* Engine stalling: Severe misfires caused by a bad coil can lead to the engine stalling, especially at idle or under load.
* Check Engine Light (CEL): The CEL will almost certainly illuminate, usually accompanied by a diagnostic trouble code (DTC) related to misfires in a specific cylinder or multiple cylinders.
* Poor fuel economy: Misfires waste fuel because the unburnt fuel is expelled through the exhaust.
* Damage to the catalytic converter: Unburnt fuel entering the catalytic converter can overheat and damage it, leading to expensive repairs.
* Hard starting: While less common, a severely degraded coil can make it difficult to start the engine.
Specific to the 1998 Ford Explorer: These vehicles often have multiple individual ignition coils (one per cylinder), rather than a single coil pack. This means a failure in one coil will affect only one cylinder, while a coil pack failure would disable multiple cylinders at once. Knowing *which* coil is bad is crucial for diagnosis and repair. A mechanic will likely use a scan tool to identify the misfiring cylinder(s) to pinpoint the faulty coil.
