This paper reports on the results of using multipoint port injection alcohol fumigation of a four-cycle turbocharged diesel engine in which the fumigation injection cycle was varied. The three cycles, dual with one-half of the alcohol injection on each engine revolution (DIT), single with all of the alcohol injected during the open intake valve revolution (SIO), and single with all of the alcohol injected during the closed intake valve revolution (SIC), lead to significant differences in the engines pressure-volume history and alcohol energy replacement tolerance. The engine was fumigated with both industrial grade ethanol and methanol and complete performance and emissions data (excluding aldehydes) were measured at low, medium, and high values of BMEP and rpm.The results help to explain recently published data showing limited energy replacement, apparent excessive rate of cylinder pressure change, and emissions for single point injection in the same engine. Additionally the results point to the limiting operational processes that control alcohol fumigation of diesel engines. Changes in the definition of knock for fumigated diesel engine operation are suggested. The dual injection cycle mode allows the widest range of energy replacement and does not produce the excessive rates of pressure rise common to single point injection and which occurs under limited conditions with SIO and SIC.Multipoint dual cycle fumigation of alcohol appears to be a viable approach to dual fueling of diesel equipment.