A natural - gas - powered engine debuted for 1995 but was not popular and was only used in fleet vehicles on a very limited production run. The Cummins B Series engine was switched from the 12 - valve to the 24 - valve (ISB) version in the middle of the 1998 model - year Dodge Rams due to emissions regulations. The ISB featured a new computer - controlled injection pump, 24 - valve head design, and an electric fuel pump.
when did dodge go to the 24 valve
in the middle of the 1998 model - year