Abstract: A method for generating a normal operation model indicative of a normal operational condition of a fuel rail of a common rail internal combustion engine. The method comprises receiving, from an engine management system of the common rail internal combustion engine via a data interface, engine model data obtained periodically during operation of the common rail internal combustion engine. The engine model data comprises fuel rail pressure data indicative of a fuel rail pressure of the fuel rail and engine speed data indicative of an engine speed of the engine. The method further comprises storing the engine model data in a memory. The engine model data is accumulated over a sampling time period.