A comprehensive investigation was carried out in order to develop the idle sound quality for diesel V6 engine when the engine development process is applied to power-train system, which included new 8-speed automatic transmission for breaking down the noise contribution between the mechanical excitation and the combustion excitation. First of all, the improvement of dynamic characteristic can be achieved during the early stages of the engine development process using experimental modal analysis (EMA) & the robust design of each engine functional system. In addition, the engine structural attenuation (SA) is enhanced such that the radiated combustion noise of the engine can be maintained at a target level even with an increased combustion excitation. It was found that the engine system has better parts and worse parts in frequency range throughout the SA analysis. It is important that weak points in the system should be optimized. In this study, the chain cover was adopted by using the passive constrained layer damping treatments (PCLDT) for the front side of 2~3 kHz range and the 3rd generation common rail system with piezoelectric injector that has a maximum injection pressure of 180 MPa was applied by using the forming cover and controlling of charging time/discharging time. Additionally, in order to reach the Euro5 standard for this engine, it is also important to adopt the low emission combustion concept with new injection strategy. However, this kind of combustion mode can give high frequency in roughness noise and worse stability in idle condition related to modulation noise. So the control of the pilot & post injection for reducing and optimizing combustion excitation in the chambers should be optimized. Therefore it has been shown that the engine development process gives the best results with respect to interior sound quality as well as to the engine radiating noise. Moreover the emotional quality of interior sound for passenger vehicle has been guaranteed.