Spark Plugs

Decide whether coils belong in a spark plug service: separate scheduled maintenance, diagnosed faults, boot kits, rail assemblies and shared-access costs.

Learn what a spark-plug resistor suppresses, why resistance is not heat range, how plugs and leads work together, and when a specification needs checking.

Learn why dry carbon collects on spark plugs, how mixture and tip temperature matter, and why black deposits differ from oil, ash and normal external stains.

Decode spark-plug part and stock numbers, compare manufacturer heat scales, and learn which code details still need a vehicle-specific fitment check.

Learn how worn or fouled spark plugs can affect starting, idle and acceleration, which symptoms need prompt help, and why symptoms alone do not prove a fault.

A misfire may feel like an uneven idle, a brief stumble or repeated jerking. Learn what to record, what else can feel similar and when to stop safely.

Wrong spark plugs can cause fit, ignition or heat-range problems. Learn which mismatches matter and what to check before running the engine again.

Understand spark plug boots, wire ends and coil boots, including serviceability, damage signs, safe handling and the limits of dielectric grease.

Choose a spark plug socket by plug profile, outside clearance, reach and retention. Learn why drive size and thread size are different measurements.

Distinguish normal electrode wear from overheating, melting and misfire. Learn what repeated spark-plug damage requires before fitting another replacement set.

Separate carbon, oil and fuel fouling from external staining. Learn what recurring deposits reveal, which evidence to keep, and why replacement alone may fail.

Diesels ignite fuel using compressed hot air. Learn how glow plugs, intake heaters and block heaters differ, and why a cold-start fault needs diagnosis.