Fuel rail
Distributes pressurized fuel to the injectors.
Along the injector row on the engine.
It connects the pressure supply to injector inlets and can carry a pressure sensor or control device.
A supply manifold feeding several spray nozzles.
Fuel-pressure instability or leakage requires checking the complete fuel circuit.
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 direct-injection rails are part of a matched pressure system, not universal tubing.
BMW combustion models; spark components are petrol-only and glow-plug hardware is diesel-only.