Making The Cummins Great Again—With A Factory CP3 Fuel Pump Swap
When Ram debuted the 2019 Ram with an all-new 6.7L Cummins three years ago, the world took notice. After all, the fresh 6.7L sported a CGI-block, stronger connecting rods, revised pistons with low-friction rings, larger head bolts and produced 1,000 lb-ft of torque. However, the one eyesore that stood out was the inclusion of the Bosch CP4.2 high-pressure fuel pump. It’s an injection pump that’s seen countless failures in LML Duramax and Nissan Titan applications over the years, and many potential Ram buyers feared the Cummins would suffer from the same reliability problems.
Fast-forward to November of 2021 and, on the heels of the world discovering that ’21 model 6.7L Cummins engines were leaving the factory with the coveted CP3 rather than the problematic CP4.2, Stellantis (parent company of Ram) issued a massive recall. The recall, which applies to more than 222,000 trucks, entails converting all Cummins-equipped ’19-’20 Ram HD’s to the CP3. Below, we’ll revisit why the CP4.2 fails so often, how catastrophic its failure can be and touch on why Ram went back to old reliable (the CP3).
1,000 LB-FT, But With A Caveat
Thanks to a host of improvements over the ’18 model year engines, which included a compacted graphite iron block, stronger forged-steel rods, revised pistons with low-friction rings, larger diameter head bolts and an earth-rotating 1,000 lb-ft of torque, the all-new 6.7L Cummins looked all but perfect on paper when it launched in January of 2019. However, the next generation common-rail Cummins did conceal one dirty secret: it was equipped with one of the most problematic injection pumps in recent memory, the Bosch CP4.2. Inclusion of this high-pressure fuel pump was a huge turnoff for a lot of potential buyers.
A Poor Track Record
The Bosch CP4.2 developed its notorious reputation in LML code Duramax V-8’s, which GM began offering in the 2011 model year for its 2500 and 3500 series trucks. Like previous versions of the 6.6L Duramax, the LML came void of a lift pump from the factory. However, whereas it didn’t seem to make a difference with the Bosch CP3—the CP4.2’s predecessor used on the Duramax from ’01-’10—a lack of sufficient low-pressure fuel supplied to the CP4.2 is said to be part of the reason why these high-pressure pumps self-destruct. Ford began offering the CP4.2 on its 6.7L Power Stroke in 2011 as well (and actually still does), but the big difference is that FoMoCo feeds it 55-psi or more of low-pressure fuel via a factory electric lift pump. To a lesser degree, many Nissan Titan XD owners experienced CP4.2 failures also, as the optional 5.0L ISV Cummins in those ’16-’19 trucks was fitted with a CP4.2.
What Fails In The CP4.2
Air infiltrating the CP4.2 remains the biggest cause for the pump’s failure. Believe it or not, improper fuel filter installation accounts for much of it (i.e. failing to fully seal the filter or failure to fully prime the system afterward). Aerated fuel allows the piston assemblies to float and they often rotate in their bores when this happens. When it does occur, the roller tappet on the bottom of the piston hits the camshaft perpendicularly rather than in a parallel manner. Soon, the metal-on-metal contact begins to wear down both components, sending shrapnel out of the CP4.2 toward the fuel injectors.
What Happens When The CP4.2 Fails
As fragments of metal leave the CP4.2’s high-pressure outlet, they contaminate the high-pressure fuel lines and eventually the injectors. Worse yet, the metal-laced fuel gets into the return circuit as well, which calls for clean or brand-new return lines and a fuel tank cleaning in addition to replacing the CP4.2, injectors, high-pressure lines and tank-to-CP4.2 lines. Oh, and the repairs can cost you anywhere from $6,000 to $10,000 or more, depending on where you take the vehicle.
The CP3 (Old Reliable)
While we aren’t aware of any widespread CP4.2 failures on ’19 and ’20 Rams, we’re sure they’re out there. Apparently in late 2020 model trucks, Ram attempted to try an updated version of the CP4.2 only to scrap it completely for ’21 models and go back to the CP3. The Bosch CP3 is a three-plunger pump while the CP4.2 features two plungers. A standard CP3 in a 6.7L Cummins application can outflow a CP4.2 by roughly 20-percent, but the CP4.2 is capable of supporting higher pressure. The CP3 was used on both the 5.9L and 6.7L Cummins common-rail engines from ’03-’18 and enjoyed a reputation for reliability (and still does today).
Not only did Stellantis, the new parent company of Ram since the FCA/PSA Group merger, find a way to revert back to the CP3 on the 6.7L Cummins engines supplied for its ’21-present trucks, but it announced a massive high-pressure fuel pump recall back in November for all ’19 and ’20 models. The recall includes more than 222,000 Ram 2500, 3500, 4500 and 5500 series trucks (222,410 in the initial NHTSA report) and entails a high-pressure fuel pump replacement (a CP3 in favor of the CP4.2), an ECM reflash and inspection or repair of additional fuel system components as necessary.
A Win-Win Scenario
In the diesel aftermarket, where the problems associated with the CP4.2 have been documented for some time, many ’19-’20 Ram owners took it upon themselves to perform their own CP3 conversions. S&S Diesel Motorsport, a leader in the common-rail fuel system world, offers one such kit. To our surprise, S&S recently made public that Ram owners who have installed its CP3 conversion can be reimbursed by the automaker, provided they produce the proper receipts and documentation.
Why No Recall From GM?
While it may be an inconvenience for some to have the recall performed, Ram is really doing its customers a solid on this one. Truck owners get a more reliable high-pressure fuel pump and one that may even last as long as the Cummins it’s fueling. But it also begs the question: why was there no recall from GM for this exact same failure? After all, the same type of failure takes place on the CP4.2-equipped LML Duramax engines offered from ’11-’16. There is no warning and the engine abruptly shuts off, which could lead to a crash…which is the reason for Ram’s issuing the recall. To be sure, a class action lawsuit against GM is still ongoing for CP4.2 failure and the manufacturer has since changed fuel system suppliers. GM’s latest 6.6L Duramax, the L5P, now also leaves the factory with an electric lift pump.
More From Driving Line
- Want to know more about CP4.2 failure? It’s number 2 on our 5 Fatal Flaws list for the Duramax.