Written By, Mike McGlothlin
Designed in the late 1990s, the fully electronic ISX15 Cummins replaced the outgoing Reman N14 Cummins. It promised to deliver cleaner emissions, better fuel economy, and even more horse power than the legendary 14.0L it was succeeding. On many fronts, the ISX15 lived up to the hype. On others, it didn't, and that gap is exactly where most Cummins ISX15 problems begin. Emissions equipment such as EGR, DPF, and SCR each presented new(and often widespread) sets of issues for fleet owners and owner operators to deal with. Then come the mechanical headaches: flattened camshaft lobes and worn timing wedges in DOHC models, crooked counterbores in SOHC versions, and exploding high-pressure fuel pumps on XPI engines. We’ll cover those headaches and more below—as well as offer sound solutions for each problem.
HIGHLIGHTS
Most Common Problems:
*Cam Lobe Wear (DOHC Engines)
*High-Pressure Fuel Pump (XPI Engines)
*Variable Geometry Turbo (VGT)
*EGR System
*Diesel Particulate Filter (DPF)
*Exhaust Aftertreatment Sensors
*DEF Doser Valve
Most Expensive Problem:
*Crooked Counterbores
*Cam Lobe Wear
*High-Pressure Fuel Pump Failure (XPI Engines)
Less-Frequent Headaches:
*Cam Lobe Wear
*High-Pressure Fuel Pump Failure (XPI Engines)
*Timing Wedge Issues
Problem #1: Cam Lobe Wear (DOHC Engines)
First and foremost, this issue is only a major concern in earlier ISX15 Cummins engines. This is one of the more common ISX15 problems reported on DOHC-era trucks. The original ISX15 Cummins featured a dual overhead camshaft design (DOHC), which carried through until 2010, when the ISX15 was redesigned as a SOHC engine. With theDOHC arrangement, the left side camshaft was dedicated to actuating the engine’s unit
injectors (i.e. camshaft-driven, unit injection). The second (right side) camshaft was used to operate the valve train and the Jacobs engine brake or, as Cummins refers to it, the Intebrake.
What Fails
Due to a production run of faulty intake rocker arms, which unfortunately were installed on the factory assembly line and that hindered oil flow, DOHC ISX15’s are notorious for“flattened camshafts.” The improperly lubricated rocker arms are known to see excessive friction. As a result, the cam rollers tend to beat up the cam lobes (as well as the roller itself), oftentimes scoring the lobes. In less frequent instances unrelated to faulty intake rockers, the camshafts themselves can spin within their respective gears (they are only pressed in from the factory). This will throw the engine’s timing off.
Solution(s)
In order to properly address the intake rocker arm issue, both the faulty rockers and the camshaft have to be replaced at the same time. It always pays to source genuine, OEMCummins components here or, at the very least, go with a reputable (and proven)aftermarket parts supplier. Additionally, it’s critical that a well-respected shop or mechanic handle the work for you, as setting the overhead, pressure-priming the engine, and other tedious tasks will need to be performed. Don’t skimp on this repair...your path toward 1million miles depends on the camshaft and valve train operating in perfect harmony.
Problem #2: Self-Destructing HPFP
Beginning with 2010 model year engines, and in conjunction with the switch over to aSOHC design, unit injection went away and the ISX received high-pressure common-rail injection. Called Xtra-High Pressure Injection, or XPI, by Cummins, the heart of the system is the high-pressure fuel pump (HPFP), a triple-piston pump that pressurizes the low-pressure fuel being supplied to it as high as 35,000-psi before passing it on to the fuel injectors. Unfortunately, the HPFP employed on 2010-2016 model year ISX15’s proved tobe a ticking timebomb.
What Fails
Inside the early high-pressure fuel pump, ceramic fuel plungers (vs. steel) were used. In short order, the ceramic plungers became notorious for failure—and when they check out it’s akin to a wrecking ball being taken to the high-pressure injection system. The ceramic plungers often break apart, but sometimes they fail catastrophically. In either case, shrapnel and debris is passed on to the injectors via the fuel rail, effectively contaminating the rest of the (expensive) XPI system. The key warning sign that a HPFP is failing typically manifests itself in the form of a low fuel pressure code being thrown.
Solution(s)
Well aware of the problem, Cummins released a redesigned HPFP with steel internal plungers in 2017, and it came as standard equipment on all 2017-later model ISX15’s. Since being introduced, the steel plunger HPFP has been installed and retrofitted onto countless early ISX15 engines. Whether you’re sourcing a late-model, steel plunger HPFP out of necessity or for peace of mind, make sure any remanufactured pump you obtain comes from a reputable dealer. Also, confirm that the HPFP is equipped with brand-new (notreused) steel plungers.
Problem #3: Crooked Counterbores
It’s unfortunate but, for any mass-produced engine, final machine work isn’t always 100-percent perfect on every component. This is one of the costlier Cummins ISX problems on the platform, and it often contributes to blown head gasket scenarios, not to mention significant downtime for the owner. In the case of the ISX, and especially the versions produced since 2010, this includes imperfect counterbore work in the block. Thanks to the all-important cylinder head to crankcase seal being inadequate on SOHC models, this problem often contributes to blown head gasket scenarios, not to mention significant downtime for the owner. Sadly, the problem of crooked counterbores is rampant on the ISX15and it takes many of them off the road before they ever reach the 500,000-mile mark.
What Fails
The primary issue with crooked counterbores is improper liner protrusion, hence head gasket issues occurring at relatively low miles. Additionally, asymmetrical counterbores force the cylinder head to press down unevenly on the liners—and the weight and force of the head can actually wear the liners into the block, damaging it. Not surprisingly, crooked counterbores also contribute to premature liner failure. Mid-stop liner failure on an ISX15is often discovered by finding coolant in the engine oil, either during routine maintenance or by the operator discovering that the oil level is rising on the dipstick.
Solution(s)
In the aftermath of any ISX15 head gasket failure, the cause needs to be determined. This means full and proper failure diagnosis performed by a trained professional or ISX15expert. Part of the repair should always include the counterbores being inspected for proper depth, and appropriately addressed if it’s required (recut, shimmed, the works). It’s up to you to make certain your mechanic and shop of choice does its homework. Thorough analysis and proper repairs ensure the same failure doesn’t occur again. Once liner protrusion is in spec and true, the ISX15 is a solid long-haul performer.
Problem #4: Oil Pump Failure
This issue isn’t an everyday occurrence with the ISX15 Cummins, but it’s common enough to warrant our mentioning it here. Still, it's one of the Cummins ISX15 problems worth understanding before it strands you roadside. After all, there is arguably nothing more destructive to an engine than a lack of oil pressure. In short order, bearings can be toast, the engine can be dead, and you’re stranded on the side of the highway. What’s worse is that an oil pressure issue can render some of the engine’s internals unusable for the rebuild. If you’ve got an aging ISX in your fleet, train your drivers to keep a watchful eye on engine oil pressure.
What Fails
Make no mistake, ISX15 oil pumps don’t drop like flies, but with age, high miles and elevated operating hours they can bite the dust at any time. We are talking 800,000 and900,000-plus miles here. Many times, the oil pump will spin a bearing, while a failed oil pressure regulator sends other pumps to the grave. If the low-pressure situation that occurs as an immediate and direct result of pump failure is caught in time, minimal engine damage is usually incurred. Unfortunately, many operators don’t adhere to the warning(s)on the dash or simply can’t get the engine shut down in short order. These latter scenarios tend to kill main and rod bearings.
Solution(s)
A new oil pump is the obvious solution. But because oil pump failure typically occurs on engines with excessive miles on the clock it pays to consider additional high-mile measures at the same time. This means deciding whether or not to go ahead with a complete overhaul. Trust us, a 900,000-mile ISX Cummins engine is due for a rebuild, not just a fresh set of main and rod bearings... By going through the block, rotating assembly, head, turbo, and fuel system, you give yourself a chance to drive an ISX another 900,000 miles.
Problem #5: VGT Issues
Throughout most of the ISX15’s production run it was graced with a variable geometry turbocharger (VGT). VGT technology allows manufacturers to reduce particulate matter(PM) emissions by keeping the engine in its peak efficiency range regardless of engine rpm.Because of this, turbo lag is greatly reduced—and so is the amount of PM leaving the exhaust. In 2003, the Holset HE551V became the first VGT Cummins used on the ISX platform. In 2007, an improved VGT, the Holset HE561VE, was phased in. After that, and from 2010-on, the HE451VE was used. Each new model came with greater technological advancement and quicker response time.
What Fails
However, the unglamorous side of VGT technology is that it’s prone to a host of operational issues. From carbon buildup and corrosion hindering the movement of the sliding nozzle to actuator and wiring problems, all three turbo models on the ISX15 Cummins (HE551V,HE561VE, and HE451VE) are known for their shortcomings in the reliability department.As for turbo actuator issues (arguably the most common problems faced by ISX15 owners),damaged pinion gear teeth and/or a seized pinion gear are leading causes, while corrosion is the common culprit behind a sticking sliding nozzle assembly on the exhaust (drive) side of the turbo.
Solution(s)
Solving a turbo actuator issue can be attempted by disassembling the unit and inspecting its internals for wear, damage, and full travel, but oftentimes complete replacement is necessary. In the latter situation, always source an OEM unit. On the other hand, corrosion issues within the turbine side of the VGT can be addressed by pulling the turbo apart and cleaning it. This should only be performed by a technician or mechanic that knows his or her way around the Holset units. Removing the corrosion and carbon buildup in the sliding nozzle mechanism can allow it to move freely again, and even a small amount of clearancing can keep future seizure events from happening.
Problem #6: DEF Doser
Selective Catalytic Reduction (SCR) technology debuted on the ISX15 Cummins platform in2009, in the form of the 2010 model year, SOHC, 2250CM engines. SCR calls for a mixture of urea and deionized water called diesel exhaust fluid (DEF) to be injected in the exhaust after treatment system to help reduce NOx emissions. DEF enters the fray upwind of the SCR catalyst and a DEF doser valve is charged with spraying the precise amount of fluid. In a perfect world, the process effectively transforms NOx into environmentally safe nitrogen and water.
What Fails
Unfortunately, the DEF doser valve is notorious for failure on the ISX15. When left over DEF deposits crystalize, they often plug up the end of the doser valve, hindering its ability to adequately distribute DEF into the after treatment system. Before it clogs up completely, its operation is made much less efficient due to this buildup, which means the NOx-to-nitrogen (and water) conversion that needs to take place in the exhaust system is no longer happening efficiently. Eventually, failure of the DEF doser to work properly leads to codes being thrown, can contribute to DEF leaks, and can even culminate in engine derate.
Solution(s)
Prior to forking over the cash for a new DEF doser assembly, a voltage and wiring check never hurts, nor does removal and cleaning of the DEF doser valve. Also make sure to give the DEF line running from the DEF tank to the doser valve a look, most notably for any blockage or leak points. Once those items check out, the purchase of a new DEF doser assembly can more easily be justified. Believe it or not, the ISX15’s DEF doser valve should be replaced every year to ensure the engine’s after treatment system continues to function flawlessly. At the very least, pull, inspect, and clean the DEF valve annually.
Problem #7: EGR Cooler Cummins ISX15 Diesel Engine Parts
Exhaust gas recirculation (EGR) technology also serves to curb NOx emissions on diesel engines, and it was along for the ride on the ISX15 Cummins long before SCR and DEF arrived (EGR first debuted in 2002). EGR-related ISX15 problems are among the most frequent complaints from over-the-road drivers. No different than those other well-meaning, emissions-reducing technologies, EGR brings a host of problems with it. The EGR valve (which routes exhaust gases back into the intake) and the EGR cooler (which is responsible for cooling exhaust gases by as much as 700 degrees F) are both prone to becoming restricted and even ceasing to function.
What Happens
With EGR on a diesel engine, carbon buildup is inevitable, especially on the intake side of things (intake manifold, intake ports on the head, etc.). Within the EGR valve specifically, this buildup takes a toll over time, restricting airflow and also inhibiting the valve’s ability to function properly. For these reasons, it’s extremely common for an EGR valve to “stick”(seize in place), and sometimes even leak. As for the EGR cooler, its constant exposure to elevated exhaust gas temperature means it needs the engine coolant passing though it to be as efficient and abundant as possible. A lack of coolant (or proper cooling) through the EGR cooler and it can rupture internally.
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Solution(s)
A lot of EGR-related issues can be avoided—or at the very least, put off until higher miles—by treating the system to routine cleanings. For over-the-road trucks that rack up big miles, this means twice a year in order to keep the EGR system on the up-and-up. Additionally, engine coolant should be regularly checked for proper health and level, not to mention flushed and replaced at the required interval. Finally, any time an EGR valve, cooler, or even sensor has to be replaced, always source a genuine OEM replacement. With proper care and repair, the ISX15’s EGR system can be made quite reliable.
Problem #8: Pressure Differential Sensors
As Cummins began pouring added (yet necessary) complexity on top of the ISX15 in order to meet tightening emissions standards, an increase in potential failure points was inevitable. Sensor failures like this rank among the more frustrating Cummins ISX15 problems since they rarely throw an obvious code. This is especially true in the exhaust aftertreatment system. There are a plethora of sensors in an ISX15 engine’s aftertreatment system, chiefly among them are pressure differential sensors. They are vital in maintaining proper functionality of both the diesel particulate filter (DPF) and exhaust gas recirculation (EGR) systems. Without them, the dash lights up like a Christmas tree, alarms go off and, eventually, you’re in limp home mode.
Why They Fail
Occasionally they cease to function due to age, but in most cases pressure differential sensors stop working as a result of their work environment. Located where heat, soot, carbon, and blow by are always present means constant exposure to the harshest conditions possible. It’s surprising these sensors last as long as they do, given their work environment.But beyond dying of “natural causes,” pressure differential sensors can fail in short order when coolant is allowed to infiltrate the engine’s exhaust system (think blown head gasket or EGR cooler), not to mention that excessive oil contamination can kill them as well. A check engine light (CEL), a downturn in engine performance, and even a derate can occur when one of these crucial sensors checks out.
Solution(s)
Not unlike many emissions-related problems, the lifespan of a pressure differential sensor can be prolonged by being proactive. That means removing, cleaning, and reinstalling them on a routine basis to remove any grime or corrosion buildup, which will serve to keep them reading accurately. Many owner-operators do this to minimize downtime in the event of an unexpected sensor failure occurring hundreds of miles from home. When it is time to replace a failed pressure differential sensor, stick with OEM or buy from a reputable aftermarket source. Additional peace of mind can be had by keeping a spare sensor (or two)in the cab of the truck.
Problem #9: DPF Failure
Diesel particulate filter technology debuted on the ISX15 Cummins for the 2007 model year to cut down on PM emissions. Its job is to collect soot that would otherwise leave the exhaust system and vent to the atmosphere. Once trapped, its job is to periodically transform accumulated soot into a fine, more storable ash through a process called regeneration, which requires additional diesel fuel—beyond what’s used for combustion—to be used.Regeneration events are either passive, active, or forced, and they’re necessary to keep theDPF alive. However, the DPF will eventually require servicing.
What Fails
There are two primary ways the DPF can fail: 1) by completely filling up with ash or 2) internal rupture. When the DPF has been filled to the brim with ash, it can no longer utilize the regeneration function to create more storage space. At this point, the DPF either has to be cleaned or replaced. When a DPF fails before filling with ash, it’s usually due to a crack in the internal core. When this happens, soot can be allowed to leak out of the DPF, and out the exhaust. For a bit of additional damage, when excessive soot is allowed to pass through the exhaust system, it can also ruin the pressure differential sensor.
Solution(s)
Thankfully, the DPF that’s part of the ISX15 Cummins’ exhaust system is 100-percent serviceable—and this is the best way to keep the DPF operating optimally. DPF-related ISX15 problems are entirely preventable with proper maintenance. Our best advice: always address any regeneration issues immediately. For most over-the-road ISX15’s, DPF cleanings should be observed every 250,000 to 400,000 miles, along with an inspection of the system as a whole (sensors, exhaust mounts, SCR components if equipped, etc.). Intermittently, a cracked or irreparable DPF is encountered during cleaning, which obviously warrants a brand-new unit, along with a much higher bill. This is a part of life for on-highway diesel owners in the post-2007 era. Our best advice: always address any regeneration issues immediately—your DPF depends on this process being carried out regularly or the DPF will fill up prematurely.
Problem #10: Camshaft Timing Wedge Issues
This particular headache applies to early ISX15 Cummins engines, versions with the dual overhead cam arrangement. Timing-related Cummins ISX problems like this one require an experienced hand to resolve correctly. In these DOHC models, the camshafts are dependent on timing wedges, of the correct thickness, to remain in perfect operation. Unfortunately, these wedges have a tendency to wear over time, which can throw off an ISX15’s timing. When the balance of the engine is thrown off, it’s immediately noticeable by an alert driver.Unfortunately, remedying the situation calls for a trip into the shop and at least a day of downtime.
What Happens
As mentioned, the timing wedges are prone to wear, which alters camshaft timing and can upset the balance of the engine. Common symptoms include poor overall performance, reduced fuel economy, and even elevated soot levels in the engine oil (via contamination due to incorrect timing). Aside from normal wear and tear, timing wedge issues are often encountered following a camshaft replacement, or after an engine overhaul has been performed. Incorrect wedge installation (or, in some cases, inferior wedges) results in camshaft timing not being set properly.
Solution(s)
Correct timing wedge installation is paramount on a DOHC ISX15, so always make sure you enlist the help of an experienced ISX mechanic with the right tools to perform all the work.Only a veteran wrench—and preferably one with experience working on the ISX—should set the timing on the engine (or reset the timing on the engine). Proper wedge seating, timing, running the overhead, all of it should be left to someone who’s done it before.Finally, use only OEM or OEM-quality aftermarket wedges. Correct engine timing is vital, which makes high-quality wedges critical.
