Spark plugs wear out as electrical voltage erodes the metal electrodes. As the gap between the electrodes widens, the ignition coil has to work harder to generate a spark. Eventually, the cylinder stops firing cleanly.
When plugs fail, you will usually feel a subtle hesitation when pressing the gas, a rough idle at stoplights, or a heavy stutter when pulling a load uphill. A engine misfire will also set off the check engine light. If the light is flashing, the engine is misfiring badly enough that unburnt fuel can flow into the exhaust and ruin the catalytic converter.
What Replacing Spark Plugs Involves
On a basic four-cylinder engine, replacing spark plugs is straightforward. On many modern V6 and V8 engines, the work takes much longer. On several popular V6 engines, reaching the rear bank of cylinders requires removing the upper intake manifold and replacing the manifold gasket to access the plugs and ignition coils.
When we pull old plugs, we look closely at their condition. Oil on the threads points to a valve cover gasket leak, while wet fuel fouling suggests a stuck fuel injector. We install original-equipment or high-grade replacement plugs, such as NGK, gapped to your engine's precise specifications. If spark plug wires are cracked or coil packs show carbon tracking, we replace them while everything is already disassembled so you do not pay for duplicate labor later.
Diagnostic Missteps
A misfire code on a code reader does not guarantee that a car needs spark plugs. A failing ignition coil pack, a bad fuel injector, or low mechanical cylinder compression will cause the same shaking and check engine light. Replacing plugs without diagnosing the root cause often leaves the real problem unfixed.
We also regularly fix job attempts where someone tried to replace their own plugs at home. On tight V8 engine bays, it