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THE RECALL YOU WANTED – Cummins CP4

A Factory-Approved CP3 Conversion For Your ’19-’20 Ram

With a CGI block, forged-steel connecting rods, updated pistons with low-friction rings, and 1,000 lb-ft of torque right out of the box, the 2019 6.7L Cummins was a dream come true for Ram fans. On top of that, its four-digit torque number was a first in the diesel truck segment, and immediately reignited the torque war with crosstown rival, Ford Motor Company. But the all-new Cummins was also no longer equipped with the tried and true Bosch CP3 high-pressure fuel pump. Rather, it’d been fitted with the new-age CP4.2, the twin-piston pump that had proven more than problematic in LML Duramax and Nissan Titan 5.0L Cummins applications.

For two model years (’19 and ‘20), Cummins-powered Rams left the factory with the CP4.2, but in a press release for its ’21 models, the automaker’s engine supplier made mention of “flow rate increases through the fuel delivery system,” which ended up being a return to the CP3. Trading the CP4.2 in for the CP3 was music to the ears of Cummins and Ram fans alike, but what about ’19 and ’20 owners stuck with the ticking timebomb? In November of last year, their prayers were answered when Stellantis—the new parent company of Ram—initiated a recall that called for all ’19-’20 models to be retrofitted with a CP3.

In the following pages, we’ll cover the massive recall, which applies to more than 222,000 vehicles, as well as illustrate how and why the CP4.2 fails.

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Like Ford did with its crankcase for the 6.7L Power Stroke, Cummins turned to a compacted graphite iron (CGI), deep skirt block in ’19 with the revised 6.7L I-6. CGI provides added hardness and fatigue strength over conventional gray iron. But on top of being stronger than the previous, cast-iron crankcase, the CGI block weighs less. Combined with a few other weight-saving measures, the overall weight of the ’19 6.7L Cummins was reduced by 60 pounds. A new alloy crankshaft, with a 10-bolt crank flange, also debuted in ’19.
Moving up and down in the bores are updated and lighter weight cast-aluminum pistons fitted with low-friction rings (compression on H.O. engines is 16.2:1). Larger diameter yet lighter wrist pins are also employed, and the piston assemblies are linked to the crankshaft by way of stronger, forged-steel connecting rods. In this photo, the outgoing ’18 model piston and wrist pin (left) is compared to the ’19 H.O. 6.7L Cummins’ piston and wrist pin
The 2019 6.7L Cummins H.O. had it all, a fresh foundation, arguably the strongest rotating assembly ever to grace a Cummins, and became the first diesel engine in the segment to turn out 1,000 lb-ft of torque. However, the high-pressure fuel pump bolted to the front cover was no CP3. Keen eyes immediately questioned Cummins’ switch to the Bosch CP4.2 given all of the catastrophic failures observed in the LML Duramax market, not to mention the fact that they fail on the 6.7L Power Stroke and ’16-’19 Cummins-powered Nissan Titan XD’s. Three short years later, the rock-steady CP3 is back in action.
Bore and stroke remained the same for ’19 (4.21-inches x 4.88-inches), but the revised, stronger block and rotating assembly provided plenty of insurance for Cummins to pursue more low-end torque. At 1,800 rpm the new Cummins could produce 1,000 lb-ft of torque, the first engine in the segment capable of doing that. Now, just three years later, Cummins and Ram have already upped the ante to 1,075 lb-ft straight from the factory.
This is where the cam lives in the latest 6.7L Cummins. The new camshaft is hollow, which contributes to the engine’s 60-pound weight reduction over ’18 models. Other components aiding and abetting the Cummins’ weight loss program are a revised oil pump and a water pump that both make use of a lightweight aluminum housing.
Most notable of the valvetrain changes for ’19 was the addition of hydraulic lifters, a first for Cummins. Their self-adjusting design meant that those 150,000-mile valve lash intervals were no longer needed. Quieter operation also satisfied the NVH goals Cummins had been pursuing for the new 6.7L.
With hydraulic roller lifters comes no means of adjusting the valves, hence the updated rocker arms on the ’19 6.7L Cummins. Interestingly enough, instances of high rpm have led to some valve float and collapsed lifter issues, so the verdict is still out as to whether or not the move away from solid roller lifters was for the best.
Along with sitting in an aluminum housing, the oil pump is also capable of flowing more than the unit used on ’18 and earlier engines. On the opposite side of the gear train, driven by the cam and located on the other side of the front cover, is where the CP4.2 sits on ’19-’20 6.7L Cummins engines.
Easier packaging, higher rail pressure capability, and cheaper manufacturing costs all play into why this high-pressure fuel pump, the CP4.2, is more sought after by engine manufacturers than the tried and true CP3 these days. The CP4.2 is the twin piston version of the CP4.1 (single piston), a high-pressure fuel pump that’s been used in millions of applications around the globe. It can produce peak pressure of 39,000 psi, which is perfect in an age when particular matter emissions have to be as squeaky clean as possible.
One major difference between the CP4.2 and the CP3 is its housing. All of the CP4.2’s high-pressure fuel circuits are external, which means no forged-steel and heat-treated housing, such as in the CP3’s case, where high-pressure internal circuits exist. Above, a bare aluminum CP4.2 case is on display at RCD Performance, a company that has studied the pump extensively and offers a 10.3mm stroker version for the 6.7L Power Stroke.
It’s hard not to look at the CP4.2 and assume Bosch was after cost-effective manufacturing by way of simplicity when compared to the CP3 it replaced. Beyond the CP4.2 being a twin piston pump vs. the CP3 being a three piston unit, there are far fewer moving internal parts in the CP4.2. Here you can see the piston and roller tappet assemblies, piston springs, plungers, heads, and a volume control valve (VCV) laid out. The only major component that’s missing is the cam.
Once a piston and roller tappet assembly has rotated within its bore, rapid fluctuations between aerated fuel and highly-pressurized fuel from up above begin ramming the roller into the cam lobe. As roller tappet and cam material both begin to break down, the pump failure soon snowballs. What’s worse is that the owner of the truck has no idea any of this is happening. There is typically zero warning when a CP4.2 self-destructs. Eventually however, there is a sudden engine stall, which could lead to a white-knuckle ride at highway speed.
The cam is what drives the pistons up and down within the bores, and is directly involved (though not the cause) of nearly all CP4.2 failures. It features two lobes offset 180 degrees from one another, which actuate the piston assemblies. We’ll show you the relationship the cam and piston assemblies share—in ideal operating conditions—in the following caption.
With a layer of diesel between them, the roller tappet that’s pressed into the bottom of each piston rides on the cam lobe in a parallel fashion. If lubrication is lost between these two components it doesn’t take long for the roller to seize.
Catastrophe strikes when a situation like this develops, where the roller tappet runs perpendicular to the cam lobe. The most common cause for this is air infiltrating the CP4.2, be it through improper fuel filter installation, failing to adequately prime the fuel system, or running the truck out of fuel. When air enters the picture, the pistons have a tendency to float and then rotate within their bores, which creates this devastating interaction between the roller tappet and cam.
By design, the entirety of the high-pressure area is contained within the CP4.2’s cylinders. However, in this diagram you can see the problem if the fuel becomes contaminated. Not only is the shrapnel-laced fuel from the cam and roller tappet directed to the high-pressure outlet and VCV, but it’s also able to infiltrate the return side, carrying contaminated fuel all the way back to the tank, where it can be pumped through again.
Although it’s rare for a CP4.2 to explode (literally), it’s not impossible. When a ’15 LML Duramax was towed into Lead Foot Diesel Performance’s Monroe, Georgia facility for a locked up engine complaint, they quickly found the problem. In this scenario of complete pump seizure, things culminated in the pump case blowing apart.
This is the aftermath of a typical CP4.2 failure, metal debris in the volume control valve (VCV) screen. On the CP4.2 the VCV is responsible for metering the flow rate of the fuel going into the cylinders. As the cam and roller tappet beat each other to death, the 80-micron screen eventually becomes plugged with metal shavings.
In the aftermath of a CP4.2 failure, the repair is both laborious and expensive. First, the CP4.2 has to be replaced (or a CP3 swapped in its place), along with the injectors, fuel rail(s), high-pressure fuel lines, and return hose. A thorough tank cleaning is also in store, and on trucks equipped with a factory lift pump that should be replaced, too. The typical starting cost for performing the job starts at $6,000 (parts and labor) but can easily run $10,000 or more, depending on who handles the work. At this point, some truck owners opt for a CP3 conversion. Dirty Hooker Diesel’s CP4 failure Repair kit for the LML Duramax is shown here, complete with a fresh CP4.2 pump included.
While the CP4.2 is neat piece of newfangled engineering, it is hard to beat the O.G. high-pressure fuel pump in the common-rail diesel world, the CP3. From a mass-production standpoint, the lower cost to produce the CP4.2 translates into a lower price for OEM engine manufacturers. This makes it an easy choice for engine manufacturers who are perpetually attempting to keep production costs down. The CP4.2 can support pressures as high as 39,000 psi vs. the CP3’s roughly 30,000 psi, but thanks its three piston design the CP3 outflows the CP4.2 by approximately 20-percent.
It seems that before the CP4.2 failure situation was ever allowed to get out of hand, Ram decided to switch back to the CP3 for the ’21 model year. In the meantime, a massive recall was announced for CP4.2-equipped ’19 and ’20 trucks on November 12, 2021. According to the NHTSA at the time of the initial report, the recall applied to Ram’s 2500, 3500, 4500 and 5500 series trucks, and 222,410 units were affected in total. Interim owner notification letters regarding the recall were mailed out on January 4, 2022.
So what’s the reason for the recall? The engine can stall due to a high-pressure fuel pump failure, increasing the risk of a crash. 2019 and 2020 Ram owners included in the recall are advised to contact their local dealership immediately. During the appointment, the CP4.2 will be replaced with a CP3, the powertrain control module (PCM) will be reflashed, and technicians will inspect and replace additional fuel system components as necessary—and free of charge.
After the ’21 model torque figures of 1,075 lb-ft were released back in the fall of 2020, rumors began circulating that Cummins had gone back to the CP3. This spy photo (provided courtesy of HDrams.com) was obtained at a dealership, and possibly taken by a potential buyer trying to decide between a ’20 and ’21 model. Thankfully, Ram’s recall will help provide peace of mind to most of the folks who purchased ’19 and ’20 model year trucks.
Before Ram initiated the recall, which is essentially a factory-backed CP3 swap, S&S Diesel Motorsport was already offering a path to improved reliability for ’19 and ’20 Ram owners. The company’s CP3 conversion is CARB-compliant (E.O. #D-756-5), comes with everything needed to perform the swap, and doesn’t even require a tuning change to be seamlessly integrated. Better yet, if you own a ’19 or ’20 truck and already performed an S&S CP3 conversion on your own dime, Ram may reimburse you for the costs incurred. Contact your local Chrysler dealer for details, or check out this link to the automaker’s reimbursement request form: https://www.chrysler.com/webselfservice/fcanorth/VinInputForm.jsp?fbclid=IwAR3YHEupHSoAxgPX60yRs4zPCtiyMTtDd1VfGkuyjHbfTf0xHISQEjZOVjI
By not covering CP4.2 failure under warranty due to a fuel contamination clause, class action lawsuits have been filed against GM (as well Ford and even Chrysler), which could end up costing the General a colossal amount of capital in the end. The first class-action suit was filed in 2018 and things picked up steam in late 2020, but appear stalled at the present time. As we went to press, a trial date for February, 2023 had been established. That may be a very long year for diesel owners who’ve experienced CP4.2 failure and incurred the costs associated with it firsthand. At the same time, it’s highly commendable that Ram issued the recall to try to get ahead of what could become an even bigger problem for ’19 and ’20 model year truck owners in time.
So now that we know most CP4.2 failures go unnoticed until the engine stalls and that such a scenario could potentially lead to the vehicle crashing, why didn’t GM issue a recall for the LML Duramax? It’s a fair question given the fact that Ram is addressing the problem before it has a chance to get out of hand. It’s also a process that will undoubtedly cost them millions.

SOURCES

Bosch
bosch.us

Cummins
cummins.com

HDrams.com
hdrams.com

Lead Foot Diesel Performance
770.267.3322
leadfootdiesel.com

NHTSA
nhtsa.gov

Ram
ramtrucks.com

RCD Performance
309.822.0600
rcdperformance.com

S&S Diesel Motorsport
ssdiesel.com

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