In a modern diesel engine, a high fuel injection pressure is achieved by a common-rail system. Therefore, it is important to understand the effects of fuel properties on engine performances because a diesel fuel could deteriorate inside an injector at such severe conditions. The test methods so far basically use the fuel with pro-fouling agent to form deposit on injector. In this study, a novel test procedure was developed to evaluate the effect of the use of the fuel with and without zinc contaminant on injector performance. With Zn doped European specification B7 fuel (7% biodiesel) as a reference, the test result showed that an engine torque decreased almost lineally over time, and the overall torque drop was 9% after 300 hours. The investigation of the dismantled injector after the test revealed that the deposit was not formed on the sliding parts of the injector, but on the nozzle hole surface. The performance of a dismantled injector after the test was examined and it was concluded that the torque drop in the engine test was induced by formation of the nozzle deposits. Then, the effect of the use of a blended fuel conforming to the Japanese specification on injector deposit formation was also investigated with the same test procedure. This fuel was blended without Zinc to meet the JIS No. 2 specification. The overall engine torque drop rate in the injector deposit formation test was 5% after 300 hours. Thus, it was concluded that the test procedure is sufficient to generate some loss in the injector performance even with non-Zinc containing fuel, although to a lesser extent compared to the Zn doped B7 fuel. In addition, unlike Zn doped B7 fuel, some periods of recovery in engine torque were found during the test, this suggests the strength of a deposit adhesion on a nozzle surface was relatively weak.