The lead wrapped method was adopted to isolate the No. 1–5 cylinders, only the No. 6 cylinder part was bared. In order to eliminate the aerodynamic noise, the exhaust main of diesel engine was connected to the outdoor by a long pipe.

The diesel engine drag test was carried out, so that the piston slap noise can be measured separately. It can be used for comparison with separated results.

The VMD-RobustICA-CWT method is proposed to separate and identify the noise sources of the 6-cylinder diesel engine. The results show that the VMD-RobustICA-CWT method has better performance than the EEMD-RobustICA-CWT method.