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2004 Dodge Ram Diesel

Originally Published in Trailer Life Magazine

To go with the new emissions regulations for the 2004 calendar year, Cummins has revamped the ISB engine used in Dodge pickup trucks. It is more powerful, slightly quieter and more efficient, and available with a manual or an automatic transmission in all 50 states.

There is no longer a choice of Standard or HO in Cummins engines in the Ram, as all carry the new rating of 325 hp at 2,900 rpm and a full 600 lb-ft of torque at 1,600 rpm, which betters the competition’s output as of presstime. Torque available at idle is about 380 lb-ft, or what most 5.5- to 6-liter gas engines make at peak torque. The Ram diesel’s standard gearbox is the NV5600 six-speed manual and the 48RE four-speed automatic, which was designed with these power levels in mind when it debuted in 2003, is optional.

Although the ISB has been capable of power ratings above these, this is the first time it has been done with the new emissions standard. And in keeping with Cummins’ simple and serviceable approach, the engine meets emissions without EGR.

Extra power generally brings more heat, which has been addressed with a new air intake and intercooler for less pressure drop and more flow. The fan shroud is mounted to the engine, allowing closer clearance tolerances, which produces better airflow. The fan-clutch programming brings it on slowly — a bit earlier than necessary to avoid the big hit of it engaging all at once.


The basic common-rail, self-priming injection system remains, but uses a new gear train for quieter operation and about 50 percent more code in the electronics for tuning. The turbocharger now uses electronic control for the wastegate actuator, a larger compressor wheel and a 4-inch exhaust system with revised gasketing systems. Inconel exhaust valves ride in stellite seats for heat resistance, and the pistons have cooling galleries within to move oil through and to keep the ring pack cool.

Service intervals have been doubled. They are up to 7,500 miles for the more severe schedule B, a result of the lowered emissions, 22,000 hours of dyno time and 1.5 million miles of road-test time.

The exhaust brake offered by the Mopar parts division that’s available for dealer installation is now certified for both manual and automatic transmissions and won’t void the warranty. The brake delivers 170 brake hp at 3,000 rpm, and we highly recommend exhaust brakes on diesels pulling heavy trailers. New logic in the automatic allows it to lock up the torque converter, under certain conditions, in fourth, third and second gears to aid control.

The 2004-½ Ram Cummins is rated for a maximum trailer load of 16,400 pounds, gross combination weight rating to 23,000 pounds and costs about $5,700 more than the price of the standard Hemi engine, or about $25 per lb-ft of torque.

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