Accurate measurement of fuel consumption is required to quantify the efficiency of an engine or predict emissions. As part of a larger project, accurate instantaneous fuel consumption data was required for a John Deere 4045T diesel engine. While establishing test criteria, it became evident that literature did not provide clear recommendations on the number of data points or time duration for data collection, for a diesel engine. Fuel consumption tests were conducted using up to 15 data points of percent fuel rate and up to 15 min of data collection. Based on statistical analysis of test results, at least 2 data points (0% and 100% of fuel rate) and 2 min of data collection are recommended for similar fuel-injected, diesel engine fuel rate tests. When a nonfuel injected engine is used, the Hogan et al. (2007) recommendation of at least 3 data points and 3.5 min of data collection should be followed.