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The XUD9 IDI 6-hour steady-state test was developed to evaluate the nozzle coking propensity of diesel fuels. After the CEC 1997 Round-Robin, it was concluded that this test could not discriminate between fuels with the statistical confidence required for CEC tests. Furthermore, it was noted that the test would have to be considerably improved if it was to have any chance of meeting the CEC statistical standards. In 1998, Texaco proposed a 10 hour cyclic test as a replacement for the 6 hour steady-state test. A Task-Force was formed to investigate whether this test was a suitable alternative. After a mini Round-Robin, using the 10 hour cyclic test method, the high potential of the test was confirmed. Dynamic fuel injection timing was identified as the single most important parameter affecting nozzle coking. Cost-effective equipment was selected for measuring dynamic fuel injection timing accurately.