Abstract: A method and apparatus for determining the absolute compression pressure of each cylinder in an internal combustion engine is disclosed. The technique involves analyzing the changes in engine kinetic energy in order to calculate both the work of compression and expansion of each cylinder in a multi-cylinder engine typically during a decelerating engine cycle. Speed data is obtained and the work associated with the compression and expansion process for each cylinder is calculated and compared to the compression and expansion data of a good engine which is stored in computer memory. If a compression fault is present, it can be detected because that cylinder will display a decrease in both the work of compression and expansion. Once a faulted cylinder has been identified, the magnitude of the fault can be calculated and normalized and the compression pressure of each cylinder calculated and displayed.