06/02/2026
Spark Plug
A spark plug is an ignition device that converts high-voltage electrical energy from the ignition coil into a spark inside the combustion chamber.
This spark ignites the compressed airโfuel mixture, creating controlled combustion that drives the piston downward and produces engine power.
๐ดWorking Principle
๐The battery supplies low voltage to the ignition coil.
๐The ignition coil steps it up to around 20,000โ40,000 volts.
๐High voltage travels through the spark plug wire or coil-on-plug system.
๐Voltage jumps across the center electrode and ground electrode gap.
๐This jump creates a spark arc (~8,000ยฐC) that ignites the mixture.
๐ Combustion pressure pushes the piston down, rotating the crankshaft.
๐ดSpark Plug Construction
Key parts:
Center electrode โ carries high voltage.
Ground electrode โ forms spark gap.
Ceramic insulator โ prevents electrical leakage and withstands heat.
Metal shell โ screws into cylinder head and transfers heat.
Resistor โ reduces electrical noise affecting ECU sensors.
๐ Heat Range Concept (Very Important)
Spark plugs must operate between 450ยฐC โ 850ยฐC:
Too cold plug โ carbon fouling, misfire.
Too hot plug โ pre-ignition, engine damage.
Correct heat range ensures:
Self-cleaning temperature
Stable combustion
Long engine life
๐Common Spark Plug Fault Symptoms
Engine misfire
Rough idle
Poor fuel economy
Hard starting
Loss of power/acceleration
Increased emissions
๐ OBD-II Trouble Codes Related to Spark Plugs
Useful for diagnostics:
P0300 โ Random/multiple cylinder misfire
P0301โP0304 โ Misfire in specific cylinder
P0350โP0362 โ Ignition coil circuit faults
P0171/P0172 โ Lean or rich mixture affecting spark quality
๐Service Life by Type
Copper plug โ ~20,000โ30,000 km
Platinum โ ~60,000 km
Iridium โ up to 100,000 km
๐Professional Tip
Always check spark plug gap, color, and depositsโ
they reveal engine health, fuel mixture condition,
ใ
