This disclosure provides system and method that can determine hydraulic start of injection (SOI) in engines using an in-cylinder pressure sensor. The system and method determine apparent heat release rate (AHRR) curve data for the cylinder from the pressure information provided by the in-cylinder pressure sensors, and the hydraulic SOI from the derivative of the AHRR curve data. The system and method provide diagnostic, control and/or compensation opportunities for fuel injector operation in high pressure fuel rail engine systems without use of expensive or complex fuel injector components.