Stringent emission regulations are forcing combustion efficiency improvement. Therefore Diesel fuel injection pressures have regularly increased in the recent years to meet emission levels. This has made the Fuel Injection Equipments (FIE) more sensitive to fuel contaminants. The control and maintaining of the Diesel fuel cleanliness is therefore a key parameter of its performance and durability.Previously, FIE protection was specified only by the filter efficiency, as defined by the ISO 19438 lab test method. But new specifications have been developed and recommended by, defining only fuel cleanliness level at FIE entrance, no matter the operating conditions or any other considerations. It was therefore needed to investigate fuel contamination sources and dynamic phenomena like vibration and viscosity impact on fuel cleanliness, and link it to acceptable filter efficiency.A lab simulation was initially developed to establish comparisons with the ISO 19438 standard test method, in term of test conditions and influence on particles retention efficiency.Test data obtained from vehicle tests have highlighted that vibrations, flow variations and driving profiles has major influence on fuel cleanliness. It was also determined that particle release phenomena was more important with “dirty” fuels rather than with cleaner ones.Therefore, this generates a new baseline for the filtration function, in order to ensure consistent FIE protection. Indeed, following filter location on the vehicle, geographical origin of the fuel, layout of the fuel feeding line, stop-start integration and even the driver profile, different filtration requirements could be expected. But it is of no suprise that the above variables always lead to higher efficiency requirements.