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Performance Roadblocks of the ’03-’07 5.9L Cummins

With the introduction of the high-pressure common-rail 5.9L Cummins in Dodge trucks for the ’03 model year, the days of mechanical injection were gone for good—but the days of making easy horsepower were just beginning. Cummins might’ve traded in their commercial grade, inline-six mill’s down-on-the-farm past for full-on electronic controls, but in doing so it gave birth to the modern diesel era. Right out of the box, the quieter, cleaner common-rail Cummins produced 305 hp and 555 lb-ft at the crank. By ’04.5, those numbers increased to 325 hp and 600 lb-ft, with torque jumping once again in ’05 to 610 lb-ft. Throw an aggressive calibration at the ECM and you can squeeze somewhere in the neighborhood of 500rwhp out of a third-gen Dodge.

But while it’s easy to coax an extra 230 hp and 450 lb-ft out of the common-rail 5.9L, it doesn’t take long to smoke the four-speed automatic transmission behind it (or the OEM clutch, should your Ram be graced with a hand shaker). Thanks to no shortage of weak links in the 48RE slushbox, it’s best to build it once and be done with things rather than nickel and dime one together and pray that it holds. After that, and if you’re campaigning an ’03 or early ’04 model, go ahead and save yourself the trouble of getting stranded and ditch the factory lift pump. From there (and thanks to your fortifying the transmission), the common-rail injection system and stock turbocharger can support 500rwhp indefinitely. However, if you want to escalate things further, turbo, injector and CP3 upgrades will all be necessary.

Roadblock #1: Automatic Transmission

Chrysler 48RE Automatic Transmission

No different from all the variations that came before it (47RE, 47RH, 46RH and A727), the 48RE has a difficult time handling the kind of torque the 5.9L Cummins can dish out. And as soon as you give in to the irresistible urge to add easy power to an ’03-’07 Dodge Ram 2500 or 3500 in the form of a programmer, all bets are off for the 48RE. An upgraded torque converter, valve body, flex plate, bands, input shaft, you name it, this thing needs it—especially once you move past 400rwhp.

Performance 48RE Parts

Dodge 48RE Performance Overhaul Kit

To stand up to the kind of power the ’03-‘07 5.9L Cummins’ stock turbo and injection system can support (again, roughly 500rwhp), several reinforcements are in store for the 48RE. First and foremost, a billet input shaft and a quality triple-disc torque converter are mandatory, along with an oversized second gear band, additional direct and overdrive clutches, a high-pressure valve body and a heavy-duty flex plate. The 48RE is one of the most popular automatic transmissions in the diesel aftermarket, but it must be properly reinforced before any type of longevity can be figured into a plan for making more horsepower.

Roadblock #2: ’03-’04 Lift Pump

2003 Cummins OEM Lift Pump

Like the ’98.5-’02 5.9L Cummins, the factory, engine-mounted lift pump is prone to failure on the ’03-’04 common-rail engines. The only difference in this case is the fact that the failed lift pump doesn’t usually take the injection pump out with it. Located behind the fuel filter reservoir, the lift pump is forced to pull fuel from the tank some 10 feet away, absorbs plenty of under hood heat and endures constant vibration. Ask it to support more fueling from the kind of tuning that makes 450-plus horsepower and you’re practically begging for trouble. To try to quell the issue, Chrysler retrofitted these early trucks with in-tank lift pumps, which live longer due to being able to push fuel to the CP3 high-pressure pump rather than pull it, along with the fact that they aren’t exposed to engine heat or vibration. Still, there are better fixes thanks to the aftermarket…

Aftermarket Lift Pump

Direct Replacement Pump FASS Fuel Systems

One of the simplest and most affordable ways to get around the failure-prone factory lift pump is to install one of FASS’s direct replacement pumps (DRP). The DRP is a direct bolt-on for under hood lift pump applications, but can also be used to replace your in-tank unit when combined with FASS’s suction tube kit. And with a flow rate of 110-gph at 16-18 psi, it not only outflows the factory lift pump tenfold, but it can support a mild injector upgrade.

Complete Aftermarket Fuel System

FASS Fuel System

To support future injector and CP3 upgrades or to better filter and remove air from the fuel feeding the engine, many ’03-’07 Cummins owners replace the factory lift pump with a complete low-pressure system. The chassis-mounted, 165-gph Titanium series system from FASS is extremely popular, can support as much as 900 hp and offers proven long-term durability. This comprehensive system’s 2-micron filtration rating keeps fuel as clean as possible and ensures those expensive common-rail, solenoid valve injectors live a long and healthy life.

Roadblock #3: Overboost Issues

Overboost Turbo Code Dodge Cummins

The quickest way to kill the fun of added power on an ’03-’07 Cummins is getting an overboost code (namely a P0234). Stock, the Holset HE341CW turbo aboard the ’03-’04 engines sees roughly 23-24 psi of boost, which is when the internal wastegate begins to open. When added fueling pushes boost beyond that, an overboost CEL causes the ECM to pull fuel and de-rate the engine by as much as 80 hp. The same thing goes for ’04.5-’07 engines fitted with the HE351CW, which could produce up to 32 psi of boost from the factory.

Boost Fooler

Cummins Electronic Boost Fooler

Boost fooling is an age-old trick that can either be executed physically (think of a mechanical pressure regulator tied in with the MAP sensor), electronically or through ECM tuning. On top of the boost fooler allowing more boost to be made without throwing a CEL, the internal wastegate has to be altered to open later. The wastegate on the HE341CW (’03-‘04) has to physically be modified to facilitate the production of additional boost. On the HE351CW (’04.5-’07), boost fooling and wastegate actuation can be handled electronically.

Boost Fooling Done Via Tuning EFI Live Tuning

While the HE351CW on ’04.5-’07 engines requires an electronic boost fooler given the fact that its internal wastegate is electronically controlled, boost trickery can also be dealt with in the ECM tuning. Some fueling boxes can provide boost fooling (such as the old-school MP-8 from TS Performance), but calibrations that are specifically written to keep the ECM from looking for any overboost scenario are most common these days. The best example of this would be through the use of EFI Live software on an ’06 or ’07 model truck.

Roadblock #4: Stock Turbo, Injectors and CP3

Common Rail Cummins Turbo Injectors CP3

Aggressive tuning, an upgraded lift pump and with the 48RE’s shortcomings addressed, ’04.5-’07 Rams can see 500 hp and nearly 1,000 lb-ft at the wheels. When treated to the same mods, ’03-‘04 trucks typically make slightly less overall power due to the smaller HE341CW vs. the HE351CW (56mm compressor wheel vs. 58mm on the HE351CW). At this point however, the stock turbo is seeing 35 psi (HE341CW) to 45 psi (HE351CW) of boost and is out of steam. In addition, the stock injectors have given everything they have to offer, as has the CP3 high-pressure fuel pump. Pushing beyond 500rwhp requires you to break ground in three different areas: turbo, injectors and injection pump.

Popular Turbo, Pump and Injector Upgrades

For a turbocharger that supports more horsepower yet keeps an ’03-’07 Dodge responsive, factory-based turbos with bigger compressor and turbine wheels or the S300 line of chargers from BorgWarner have long been go-to options for 5.9L owners. A 62mm or 63mm S300 (i.e. S362, S363) yields great drivability, towing manners and can support north of 650rwhp, with Borg’s newer SX-E versions such as the S369 SX-E showing promising results, too. Injector upgrades typically run the gamut for common-rail 5.9L owners, with 100hp units being a great entry-level option but 60 to 100-percent over injectors (200+ hp) also being regularly chosen and dialed back via ECM tuning in order to allot for future horsepower growth. The most common CP3 upgrade is a 10mm stroker pump (shown above), a direct replacement for the stock unit but that can support up to 800rwhp.

Curious what stands in your ’98.5-’02 Cummins’ way of making more horsepower? Find out how to overcome your performance obstacles here.

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