For the failure on fire surface of cylinder head for a heavyduty diesel engine at high altitude, the hypothesis that the increase of impulse frequency led by incylinder fluctuation was the failure reason was put forward. Then the incylinder pressure signals at different altitudes were collected at a plateau simulation test bed for a single cylinder engine and the ensemble empirical mode decomposition (EEMD) was conducted. Different frequency components of incylinder signal were extracted and their power spectral densities were carried out in each condition. It was found that the energy of high frequency components increased with the increase of altitude by analyzing energies of extracted different frequency components. Accordingly, the proposed hypothesis was feasible.
