A study has been done to determine the effect of changes in diesel injection timing on engine performance using a multicylinder, turbo-charged diesel engine fumigated with ethanol. Tests at half load with engine speeds of 2000 and 2400 rpm indicated that a 4% increase in thermal efficiency could be obtained by advancing the diesel injection timing from 18 to 29 °BTDC. The effect of changes in diesel timing was much more pronounced at 2400 rpm. Advancing the diesel timing decreased CO and unburned HC levels significantly. The increase in NO levels due to advances in diesel timing was offset by the decrease in NO due to ethanol addition.