Introduced in 1998 as a 14.9 litre diesel engine, the Cummins ISX was originally marketed for the heavy-duty truck market. Coincident with the EPA 2010 emissions regulations, a 14.9 and 11.9 litre version is available; known as the ISX15 and ISX11.9 respectively. The ISX11.9 (also known as the ISX12) became available for the motorcoach market, replacing the Cummins ISM.
The engine originally featured two overhead camshafts. One drove the high-pressure fuel injection and the second operated the intake and exhaust valves, with integration of an engine brake available. The 2010 ISX features a single overhead camshaft with the XPI fuel injection system which eliminates the need for a second camshaft. The ISX also features a variable Geometry turbocharger and cooled EGR. Combustion temperatures were lowered for 2010 to reduced emissions and optimized fuel economy. The engine uses Cummins' integrated electronic controls which were re-calibrated in 2012.
Cummins intended for the ISX to meet EPA 2010 regulation without using selective catalytic reduction (SCR), however this decision was reversed in late 2008. According to Cummins, it was because of new developments in the technology with the use of copper zeolite. The ISX15 was awarded EPA 2010 certification on January 8, 2010, while the ISX11.9 was awarded EPA 2010 certification on July 20, 2010.
By the 2020 model year, most of the major bus manufacturers began offering the updated version of the ISX12, called the X12.
- Cummins ISX. Diesel Power. Retrieved on 18 June 2009
- Berg, Tom (27 January 2012). Cummins Retunes ISX11.9 for Better Economy, Renames It ISX12. Power Systems Research. retrieved on 23 April 2012.
- Carretta, Justin (13 August 2008). Cummins to use SCR across the board in 2010. FleetOwner. Retrieved on 14 June 2009