The article presents the methodology of testing Continental/Siemens VDO piezoelectric injectors. To determine the correctness of their operation, the reference characteristics were used, which, due to the lack of guidelines from the manufacturer, constituted the only reference base for the obtained expenses and the intensity of fuel overflows. Simultaneously, the phase of the active experiment was simplified by limiting the number of measuring points, and then estimating the missing data using the Aitken iterative technique. Automation of the calculation process was obtained thanks to the proprietary numerical algorithm, whose formulas were introduced into a standard spreadsheet.