The smoke is generated with the incomplete combustion because of the form of the nozzle injection and irregular spray pattern as the carbon of the injector nozzle tip is generated due to the long time use of the common rail engine injector. In order to solve this kind of problems, the injector of the common rail engine is taken out to remove the generated carbon by the disintegration and cleaning of the nozzle tip part. The result that the exhaust fumes generation amount is remarkably decreased was confirmed with the improvement of the normalization of the spray pattern of the injector and incomplete combustion compare before the carbon is removed.