Dodge Cummins 2nd Generation Mechanics.
Because of changes in emissions rules, demanding 60% fewer particulates per brake horsepower-hour, the Cummins 5.9 turbo-diesel needed numerous changes for 1994, including a new fuel injection system and the first use of a catalytic converter on a Ram diesel. There were 2 versions of the 5.9 Cummins in 1998, a 12 valve and a 24 valve. The 12 valve is sought after by most folks. It got fabulous fuel mileage considering. The 24 valve engine made considerably more power but at the expense of reliability and fuel mileage.
If you have a 12V engine, don’t give it away. They are a very long life diesel engine and most will see 500,000 miles properly maintained.
The higher pressure in the newer fuel injection system atomized the fuel into finer droplets, which burned more completely and reduced particulate emissions (also increasing fuel economy). Individual plungers for each injector were operated by a camshaft through roller followers (both cam and followers were oil-lubricated). Injection timing and amount were controlled by the throttle position which was modified by a centrifugal governor moving a gear rack in the high pressure pump. The rack rotated sleeves with variable width slots that were concentric with the pump plungers. The location and height of the slot exposed to incoming fuel corresponded to the start and duration of injection. When the engine was shut off, the slot closed completely by an electric solenoid on the outside of the pump.
The fuel pump limit on wide-open throttle idle speed was raised from 2875 to 3000 rpm for improved drivability. This control made the high speed fuel cut-off more gradual as well. The new pump was also more reliable. A high-pressure piston-type lift pump had greater flow to help cool the high pressure pump. It supplied fuel to the high pressure pump at 211 bs/in2 to assure that the high speed pump was always full. An external priming plunger was included to aid in restarting after running out of fuel. An improved fuel filter (between the lift pump and high-pressure pump) and larger water separator accommodated the higher fuel flow rate; a new 100-micron strainer between the gas tank and fuel lift pump removed particles, as well. This included a thermostat-controlled fuel heater to prevent waxing in cold weather.
Throttle response and low speed torque were improved by adding a waste gate to the turbocharger and the use of a smaller turbine wheel and nozzle which reached peak boost quickly and at lower engine speed. The waste gate opened at high engine speed to prevent excessive turbine speed which would have been detrimental to turbocharger durability. The waste gate was actuated by intake manifold pressure working against a spring-loaded diaphragm. High altitude performance was unaffected by the waste gate.
Midyear 1998 thru 2002, a 24-valve head replaced the old 12-valve head, and a new electronically controlled fuel injection system replaced the mechanical system (both used high pressure direct injection). The 24-valve heads not only increased airflow, but allowed for vertical injector mounting over the center of the piston bowl for improved combustion, low-end torque, and responsiveness.