Spark plug
Starts combustion with an electrical spark.
Threaded through the cylinder head into a petrol combustion chamber.
Voltage jumps the electrode gap to begin a flame in the compressed air-fuel mixture.
A tiny timed lighter inside the cylinder.
Worn, fouled or damaged plugs can cause misfires; coils, fuel and compression can do the same.
Plugs and filters use engine-specific service guidance. Pumps and injectors are normally assessed through pressure, leakage and electrical tests.
Spark-plug service is usually less involved than direct-injector or high-pressure-pump replacement; coding and access can add work.
BMW petrol engines use spark plugs; diesel glow plugs serve a different purpose.
BMW spark-ignition petrol engines, including the combustion engine in petrol plug-in hybrids. Not diesel engines or battery-electric drive units.