The never-ending concern on the air quality and atmospheric pollution has paved way for more stringent emission legislations. Existing Diesel engine hardware face several problems on meeting the tough emission limits and they require more additional features to comply with the emission standards. The current research work throws light on the air path control approach to meet the BS4 emission norms on 2.2l SUV engine operating with EGR cooler and the techniques followed to meet the same emission norms without the application of EGR cooler which was successfully implemented on the vehicles enabling reduction of hardware. Also the migration of 2.2l engine from 88kW operating on CR 18.5 to 103kW at a lower CR of 16.5 is a challenging process to achieve NOX reduction at part loads. Optimization process included modification of various injection parameters like Main injection retardation, Increase of rail pressure and pilot separation along with adjustment of exhaust gas quantity from EGR and regulation of boost pressure. The absence of EGR cooler on the other hand increased the temperature of combustion chamber resulting in higher NOX emissions and reduced CO and HC emissions. The methodologies involved to meet the BS4 emission norms with comfortable margin achieving favorable NOX – PM trade off were thoroughly examined in this work.