The effects of engine operating conditions and fuel properties on diesel exhaust emissions and the effect of an additive on fuel-injector deposits were studied using four diesel engines.The test engines were swirl chamber type diesel engines for Japanese passenger cars: two with 1800cc. displacement, one with 2400cc displacement, and one with 2800cc displacement. Diesel exhaust emissions were collected using a dilution tunnel system, and concentrations of CO, HC, NOx and particulate were measured. Test fuels were formulated with emphasis on distillation properties (10% and 90% distillation temperatures), composition (aromatics content), and cetane number.CO, HC, NOx, and particulate emissions varied from one engine to another. The differences in these emissions among the test engines were notable at Sow load driving conditions. Regarding fuel properties: %CA considerably affected CO, HC, NOx, and particulate emissions. Also, 90% distillation temperature influenced particulate emissions, depending on engine type. Fuel injector deposits increased particulate emissions but certain detergent type additives had the effect of cleaning up injector deposits.