Emission tests were conducted on a Mack MH613 heavy duty truck equipped with a 1986 specification Mack EC-6-350 engine. The engine was equipped with the Garrett exhaust aftertreatment system. The tests were conducted by CARB (California Air Resources Board) and Garrett at the CARB El Monte, Calif. facility on a chassis dynamometer.Emission tests were also conducted on a 1989 specification 14 liter 310 HP six cylinder engine in a test cell using the EPA transient cycle. Those tests were conducted at a different facility.Tests were conducted without a particulate trap, with an uncatalyzed trap, with a catalyzed trap and with an uncatalyzed trap and fuel additive. Low sulfur (0.05%) fuel was used, except for a single test run on 0.20% fuel.With the CARB 8 point test cycle, results cannot be directly compared to those obtained using the EPA transient cycle. However, the results appear to be representative and trends should be accurate.Results of both tests show a dramatic reduction in particulates using an uncatalyzed wall flow trap. It is not clear at this time why such a large reduction was obtained. Little reduction was shown for the particular catalyzed trap tested. Use of a fuel additive, in conjunction with an uncatalyzed trap, also produced a dramatic reduciton in particulates and also enhanced regeneration performance.Results show that both engines tested should meet 1994 emission requirements of HC, CO, NOx and particulates when equipped with the aftertreatment system using an uncatalyzed wall flow trap.