In the article, the concept of technical diagnostics in relation to marine engines was characterized. The compression ignition piston engine was presented as a diagnostic object. The next part of the article discusses the composition of exhaust gases with particular emphasis on compounds harmful to the environment. The available test methods for exhaust composition are also briefly described by means indication of the engine and exhaust gas analyzer. The reduction of emission of harmful compounds in the exhaust gases is also described in the article. The main part of the article presents the research object, i.e. the marine diesel engine piston and the exhaust gases analyzer, as well as tests carried out. The tests were performed for the engine in working order and inefficient condition in order to compare them with the simulated damages of injection pump and turbocharger. The article was completed conclusions.