Cummins History, Lesson 3: ’98.5-’02 5.9L

By the late ‘90s the era of electronically controlled diesels was upon us. As the deadline to meet stricter emission regulations neared, Cummins developed the 5.9L ISB to power all Dodge Ram 2500 and 3500 trucks beginning by January 1, 1998. Sure the new I6 shared some of its hard-parts with the late 12-valve mill (such as the crankshaft, 12mm main cap bolts and connecting rods), but it would debut a 24-valve cylinder head and replace the mechanical P-pump with the electronically controlled VP44 injection pump. The result of the four-valve head and VP44 combination was substantially improved airflow, more precise fueling, improved overall drivability, reduced emissions and an increase in power.

Though the VP44 would earn a reputation for being unreliable, the 5.9L ISB (often referred to as simply the 24-valve) was a workhorse of an engine. At the time it was introduced midway through the ’98 model year, its available 235hp and 460 lb-ft torque rating bested Ford’s 7.3L Power Stroke and sat at the top of the torque war heap until Ford launched its Super Duty line for ‘99. But the more powerful and efficient Cummins wasn’t without its fair share of issues. Aside from the aforementioned VP44 (and lift pump) issues, Brazilian-cast “53” blocks would become infamous for cracking and—just like ’89-’98 engines—the killer dowel pin could still strike at any time.

Cummins’ next step into the modern era would entail the 305hp common-rail 5.9L. You can read all about it in our next installment.

’98.5-’02 5.9L Hard Facts

More Valves, More Power, Cleaner Emissions

Bringing electronically variable timing advancement into the mix, the ’98.5-’02 5.9L ISB Cummins (the ISB acronym standing for Interact System, B series engine) did away with the mechanical P7100 injection pump in favor of the Bosch VP44. The other big news was that the ISB added a 24-valve cylinder head to the equation. The newfound gadgetry and airflow improved emissions, drivability and overall power output for Dodge Ram 2500 and 3500s. To put things into perspective, it helps to remember that ¾-ton and larger pickups weren’t always the mythical, 40,000-pound GCWR creatures we know them as today. Long before Ram, Ford and GM were inching closer and closer to the 1,000 lb-ft threshold, Dodge and Ford were locked into a race to 500 lb-ft in the late ‘90s. After Cummins leap-frogged the non-intercooled 7.3L Power Stroke’s 225hp and 450 lb-ft figures with the 5.9L ISB’s 235hp, 460 lb-ft rating, Ford and Navistar responded with a 500 lb-ft version of the 7.3L. Not to be outdone, Dodge offered a high output version of the ISB roughly one year later (for ’01-’02 models), which upped the ante once again to 245hp, 505 lb-ft.

If It Ain’t Broke…

With the forged-steel crankshaft being carried over from the late 12-valve engines, the rod journals were the same, which meant the same, proven forged-steel I-beam connecting rods were employed in ISB engine. Never a weak link, they’re arguably the strongest rods to ever grace this series of engines. In fact, when these rods are treated to shot-peening and micro-polishing, they’re known to stand up to 1,400hp or more, which has made them a budget-friendly option for countless competition engine builds over the years.

Revised Pistons

The ISB 5.9L’s pistons were still made from cast-aluminum, but with the 24-valve head and centrally-located injectors, a different spray pattern was used. As well, the fuel bowls were amended to match the new injector spray pattern, thereby maximizing the combustion event (and minimizing particulate matter). Compression checked in at 16.3:1 on all standard output engines, while the high output mills released in ’01 were treated to 17.2:1 pistons.

Four-Valve Head

Four-valve cylinder heads have always been a great way to squeeze more performance out of a given engine’s displacement and the ’98.5-’02 Cummins is no different. The cast-iron, 24-valve head provided for touchier throttle response, a broader torque curve and Cummins was also able to improve coolant flow substantially over what the 12-valve head had offered. The 24-valve head featured 60 ppi valve springs, reshaped exhaust ports for improved exhaust flow and six 12 mm head bolts per cylinder. A one-piece valve cover with a reusable gasket also replaced the 12-valve’s six individual units, which simplified servicing and accessing the valvetrain. The original valve cover was red and silver and made of aluminum, but a black and silver cover made of magnesium was introduced on ’00 model engines.

Updated Cam, Longer Push Tubes

As for the rest of the valvetrain, a new camshaft was introduced with wider lobes. With the 24-valve making use of an electric lift pump (vs. a mechanical unit on the 12-valve), the cam was void of a lobe being dedicated to actuate a lift pump. Longer push tubes were also employed, along with solid mushroom tappets similar to what was used in the 12-valve.

More Efficient Oil Pump

Coinciding with the added horsepower and torque, the 24-valve received a redesigned oil pump with increased capacity. In addition, excess oil was now returned to the suction side of the oil pump instead of being sent back to the pan. The improved oil pump yielded approximately 10 psi more oil pressure across the rpm range.

Bosch VP44

For more precise control over the injection system, the electronic Bosch VP44 replaced the mechanical P7100. The rotary (distributor style) pump is similar to the VE unit employed on ’89-’93 engines, but instead of utilizing one pumping plunger it makes use of three. Just like the 12-valve 5.9L Cummins mills that preceded it, it’s driven off of the front gear train. The fixed position mounted VP44 also uses an offset keyway and is driven at half the speed of the engine. Thanks to its integrated ECU, the VP44 does more than simply pressurize fuel. It controls injection timing and volume, while also monitoring its operation. However, being that the ECU is cooled by fuel, any lack of supply pressure can damage its internal circuit board (as well as the pump itself).

Electric Lift Pump

The job of supplying fuel to the VP44 was left in the hands of a self-priming, Carter electric lift pump mounted on the driver side of the engine block. Thanks in large part due to vibration, this pump is notorious for failure, and when it dies the VP44 is no longer supplied the fuel it needs to cool and lubricate itself. It was once common practice for many Dodge dealers to install an in-tank lift pump any time a VP44 was replaced under warranty. The in-tank pump proved more reliable, but complete, externally-mounted aftermarket fuel supply systems (such as FASS or AirDog systems) have proven even more durable. As a general rule of thumb, the VP44 requires at least 5 psi worth of supply pressure to live a healthy life (although 10 to 15 psi is recommended).

Higher-Pressure, Mechanical Injectors

Although the VP44 added electronics to the injection system, the injectors remained completely mechanical. They were, however, relocated vertically over the top of each cylinder so as to spray directly into the center of each piston. The repositioning of the injectors (along with the revised piston design and a higher, 4,500 psi pop-off pressure) provided for a more even fuel spray pattern and further optimized combustion. As you can see here, even though things are busier with four valves occupying the area above each cylinder, the head’s design allows the injectors to be removed without disturbing valve lash.

HX35 vs. HY35

Carried over from the ’94-’98 12-valve engine, the wastegated, journal bearing Holset HX35W was used on all 5.9L ISBs with a manual transmission and ’98.5-’00 engines with the 47RE automatic. However, for emissions purposes automatic-equipped engines were fitted with the HY35W in ’01 and ’02. The HY35W proved more restrictive on the exhaust side, which led to quicker spool up but less flow at higher rpm. The HX35W was the opposite: slower to light but with freer flow (more horsepower capability) at higher rpm. Both turbos use a T3 turbine inlet flange, but the HX35W’s is divided while the HY35W’s flange is non-divided.

The H.O./NV5600 Option

If you opted for a manual transmission (five-speed NV4500) in ’98.5 or ’99, you got the ISB with a higher horsepower and torque rating than what was used behind the automatic (235hp and 460 lb-ft vs. 215hp and 420 lb-ft). However, beginning on ’00 model Rams, the same 235hp, 460 lb-ft engine was used across the board. Then in ’01, thanks to a higher compression ratio (17.2:1), different injectors and a more aggressively fueled VP44, a high output version of the 24-valve was introduced. The high output 5.9L ISB made a class-leading 245hp and 505 lb-ft of torque, but was only available with a six-speed NV5600 manual, which utilized a larger diameter flywheel and clutch than what was used with the NV4500.

The “53” Block

Despite all of the 24-valve engine’s advancements over the 12-valve, it had one uncorrectable flaw: Certain ’99-’01 model year blocks were prone to cracking. Approximately 100,000 crankcases, produced by TUPY, were cast with thinner water jacket walls than what was found on earlier and later model engines. The problematic blocks are identifiable via a “53” casting number visible on the driver side front of the block (but can also be located on the passenger side). Cracks typically begin beneath the freeze plugs, which can lead to coolant leakage when the engine is worked hard or exposed to increased cylinder pressure. These blocks are not guaranteed to crack, but it was a big enough problem that Dodge replaced more than its fair share of ISB short-blocks under warranty (and at times, due to Cummins getting involved in individual cases).

KDP (Carnage Still Lurks)

Once again, the killer dowel pin is something to be feared with this engine. As explained in Parts 1 and 2 of this series, the steel dowel pin that’s used to precisely align the timing gear housing at the factory can back out years (even decades) down the road and cause all kinds of internal engine damage. To ensure the dowel pin never has a chance to cost you an engine, it’s wise to dig into the front gear train and lock it in place by way of one of the various KDP fix-it kits available in the aftermarket.

Want to know how to get the most out of your '98.5-'02 5.9L Cummins? Read through our budget diesel mods!