A test technique to monitor the quality of the fuel in terms of injector nozzle deposit formation has been developed.Injector nozzle deposit is accumulated by fitting injectors to a bench mounted production engine coupled to a dynamometer. The engine is operated according to a simple run/shutdown duty cycle. At the termination of the test, the effect of the deposit on the flow characteristics of the injector nozzles is established. In the case of an intermittent type of injector, the flow is measured. In the case of a continuous type injector, the spray pattern is evaluated.