The complexity of the deposit formation process on the components of compression ignition engine, including high-pressure injection Common Rail systems, is gaining global significance. Knowledge related to the mechanisms of their formation and chemical composition is still insufficient and requires further studies. The studies allowed, hypothetically, assuming several mechanisms of their formation, but each of them requires further research in order to be verified and finally confirmed. This is due to high complexity of the factors and conditions that may affect the initiation of the deposit formation, of which the most important are: fuel and additive composition and type of contaminants from fuel production and transport. Deposit physical nature may vary, as it may be soaps, salts of metals or ashless materials like imide or amide of organic polymers. This article contains the results of the research on the assessment of Common Rail injector components contamination and their technical condition, after 80 thousand km operational run, with the use of diesel and biofuel B10.