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Electro-hydraulic injectors (EHI) are the most vulnerable components of the common rail injection system of a modern diesel engine. As a rule, the injectors’ diagnostics begins with the analysis of data of the automobile scanner. These data include the current of the high-pressure pumpmetering device, adjustment of fuel pulsewidth when balancing the engine cylinders. A comprehensive analysis carried out by means of a car scanner can be possible only if a pressure sensor is positioned in the control chamber of the injector of the common rail injection system. There are such systems, however the majority of cars, not equipped with them. The scanner data may be influenced by the technical state both of the engine and of the metering device. Consequently, it can be impossible to assess the technical state of the injectors only by means of the car scanner data. It is known that the technical state of the common rail injector is characterized by such indicator as individual fuel back drain. There is a method of measuring the injectors’ individual leakages by back flow measuring, but it can be applied only if there is an access to individual drain nozzles of EHIs. In many existing common rail injection systems the injectors are located inside the engine, the access to them is hindered. Respectively, only the common return line access is available. High-quality diagnostics of injectors in such systems is possible only with the use of specialized testers, which inevitably leads to increased costs conditioned by disassembling and fitting. To reduce the time of diagnosing electro-hydraulic injectorssignificantly, a method of determining their individual backflow by the common return line was developed.

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