What a spark plug actually does
A spark plug is the gap that lights the mix. Center electrode, ceramic, shell, ground electrode. The coil supplies the kilovolts. The plug is not the coil and not the injector.
People treat this like the coil. Or like an injector still spraying in the hole. It is neither. A spark plug is the gap. The coil — or a coil-on-plug sitting on the well — throws kilovolts down a boot. Those volts jump.
The pulse hits the center electrode. Ceramic keeps that rod off the shell. The shell is the ground path, threaded into the head. Across a measured gap sits the ground electrode. The jump ionizes the mix. That kernel is the light-off. Heat range is how fast the shell dumps heat into the head, not a hotter spark. The plug is not the coil. It is not the injector.
A fouled tip, a worn gap, a cracked insulator — those misfire. The scanner names a cylinder. Do not start at a four-pack of coils because the box said misfire. Start at the gap that was supposed to jump.
