Fuel Rail

On port injection engines it works at a few bar; on direct injection petrol engines at over 100 bar; on diesel common rail at well over 1,000 bar. A pressure sensor on the rail tells the engine control unit the actual pressure. Rails on high-pressure systems are forged steel and use special fittings.

The fuel pump fills the rail, which acts as a reservoir so every injector receives the same pressure.

Low rail pressure causes hard starting, lack of power and lean fault codes. High-pressure systems must be depressurised before work and fuel lines often must be replaced, not reused.