The question of interaction of schemes of diagnostics of engines by methods of non-disassembled control is considered, the analysis of existing methods is executed, and the use of the complex approaches increasing reliability of work of engines is offered. Methods of non-detachable diagnostics with modeling of deregulation of engine systems during operation and diagnosing the initial stages of structural and functional malfunctions are analyzed. The analysis allowed to determine the direct diagnostic parameters that unambiguously characterize the state of the object and indirect, associated with direct functional dependencies, and identify the most effective, in terms of determining correlations - direct diagnostic methods, which include, for example, indication of the working process in the engine cylinder. A relatively simple scheme of measuring and determining signals from several diagnostic elements simultaneously is proposed, from which we can conclude that information from one measurement channel can comprehensively characterize the technical condition of several elements of engine mechanisms or systems: vibration method, acoustic method, gas chromatography methods, indirect indication by determining the stress in the studs of the cylinder head, assessing the level of wear of parts on the metal content in the engine oil, as well as diagnosing the parameters of the uneven speed of the crankshaft. Analysis of methods and techniques for diagnosing internal combustion engines led to the conclusion that the method of diagnosing the uneven speed of the engine crankshaft is a promising direction in the development of methods of non-demountable diagnostics of internal combustion engines. residual life and monitor the technical condition of the engine.