Spark Plug & Ignition Service

Spark plugs are routine maintenance right up until they are not.

Worn spark plugs, failing coils, damaged boots, an incorrect gap or simply the wrong plug for the engine will produce misfires, rough running, hard starting, reduced power, a check engine light and worse fuel economy. Most of that develops slowly enough that people adapt to it without noticing.

Doing spark plug service properly means using the plug your engine actually specifies, at the correct gap, torqued to specification. Modern engines are particular. A Civic, an EcoBoost and an Audi 2.0T each want something different, and turbocharged and supercharged applications are especially unforgiving of a substitution that looks close enough.

We also check misfire data and coil circuits rather than assuming spark plugs are the whole story. If something else caused them to wear or foul, replacing them alone is a temporary fix. On many engines this job also gives us a look at conditions we would not otherwise see, including oil in the plug wells, coolant intrusion or early signs of a cylinder that is not keeping up with the others. If anything looks unusual, you will hear about it with a photograph attached.

If spark plugs come out looking wrong, that is information worth acting on.

Oil fouling points at valve seals or piston rings. A wet plug suggests a fuel or injector problem. Heavy carbon can indicate a rich condition. Damage to the electrode may mean detonation, which is a tuning or fuel quality issue rather than an ignition one. Plugs that failed early on one cylinder while the rest look fine tell a different story again.

A misfire is a symptom with a long list of possible causes beyond spark plug wear. Coils, wiring, plug gap, compression loss, injector performance, vacuum leaks and control signals all produce one. Replacing spark plugs and coils is the common response and it works often enough to seem reasonable, but when it does not, the underlying cause was never addressed.

Turbocharged and high output engines put more demand on the ignition system, which is why correct spark plug specification and a sensible interval matter more on those than on a naturally aspirated engine.