A large number of current commercial off-the-shelf (COTS) diesel engines available to the U.S. Military employ High Pressure Common Rail (HPCR) fuel injection systems. Overall performance and endurance of these HPCR systems has the potential to vary with use of military or alternative fuels. Testing was conducted using the Ford 6.7L diesel engine to determine the impact on engine and HPCR fuel system performance with the following test fuels: diesel (ULSD), JP-8, 50%:50% volumetric blend of JP-8/Synthetic Paraffinic Kerosene (SPK), and 100% SPK. The U.S. Army 210-hr Tactical Wheeled Vehicle Cycle (TWVC) engine endurance test was used to determine engine and HPCR system performance. Engine performance over the test duration, pre- and post-test powercurves and post-test fuel injection component inspections were used to determine each fuels performance.