This work is an experimental study where knock sensor placements are investigated using engine tests. The aim is to studythe quality of the signal from knock sensors and how the signal for engine control is affected at different sensor locations on Scanias, engine DC13. To find out at witch position on the engine youcan get a usable signal for engine control, the engine is running while the knock sensors with advanced measurement equipment is connected to the engine. Evaluation of signals from the knock sensors are made in the computer program Matlab. The program is producing a seriesof plots, from these plots it is visually possible to draw conclusions and find connections.