The design and development of modern internal combustion engines is marked by a reduction in exhaust gas emissions and increase in specific power and torque. This paper aims at the study of noise reduction in 4-stroke common rail direct injection engine at idle speed. Idle speed is basically a speed of engine when vehicle is not running i.e. not in motion. Now a day, this situation often comes at red-lights, in traffic and in waiting while parked outside a business or residence etc. This paper presents a study about the effects of Fuel Injection Pressure on the combustion process.