The operation of a 350 horsepower diesel truck engine was monitored during laboratory tests using the vibration of the block to detect faults in the cylinder pressure and bearings. Simulated faults were introduced into the engine to determine the sensitivity of the vibration measurement location to a particular fault. The head bolt vibration signal was found to be the most sensitive to changes in the cylinder pressure. Single channel signal processing using cepstral windowing was able to reconstruct the cylinder pressure signal from a local head bolt vibration signal. The lower block vibration signals were more sensitive in detecting a main bearing fault. However, in this case complex signal processing using multichannel inverse filtering was necessary to identify the location of the fault. The application of vibration monitoring to in-service diagnostics is discussed.