Cummins Turbodiesel Problems

Common 5.9L & 6.7L Cummins Diesel Engine Problems

No machine is perfect, and despite a largely favorable and somewhat fabled reputation, the Cummins turbodiesel found in 1989 to current Dodge/Ram trucks is not without certain flaws, annoyances, and otherwise lackluster design features. While some of the common problems and fatal flaws listed herein do not necessary coincidence with the Cummins engine, they contribute to vehicle reliability concerns nonetheless. Here's our list of common problems found in Cummins equipped Dodge and Ram pickups. The following items are loosely organized in chronological order, starting with the 6BT and ending with the latest 6.7L Cummins.

12v Cummins Killer Dowel Pin (KDP)

A dowel pin used to align the gear housing to the front of the engine block on 12 valve (6BT) Cummins is arguably the most infamous and well known downfall of this prized engine platform. Termed the "KDP", or "Killer Dowel Pin", heat cycles and vibration have a tendency to work this small pin out of its bore, free falling into the geartrain for the camshaft and fuel pump. In some instances no damage is caused and the pin simply dances to the bottom of the gear cover where it poses no threat. For the less fortunate, the pin becomes lodged between the camshaft and fuel pump gears, starting a chain reaction of events that results in serious, if not fatal engine damage. While the dowel pin is also used on later 24 valve (ISB) engines, failures related to KDP dislodging are generally isolated to 12 valve engines (1989 - 1998), with 1994 to 1998 model year trucks believed to be at the highest risk.

But just how common are KDP related failures? While we can't say with certainty what percentage of pins will eventually become dislodged over the course of an engine's usable lifespan (nor the amount of casualties experienced), the problem is significant enough that Cummins has its own fix to prevent such occurrences. A small tab installed over the dowel pin using an adjacent bolt maintains its position and prevents it from backing out. The aftermarket has also responded with a variety of solutions and you can obtain a complete repair kit in the $60 to $120 range while the tab itself can be purchased for under $10. A typical repair solution includes a new front cover crankshaft seal and associated gaskets/hardware in addition to the KDP tab.

For more information, see: 5.9L Cummins 12v KDP and/or 12v Cummins KDP Installation Procedures

24v Cummins #53 Engine Block Cracking

#53 block castings found on 5.9L Cummins turbodiesels are somewhat renowned for cracking due to inherently thin casting thicknesses of the water jackets. The cracks generally propagate to several inches in length and result in a significant coolant leak. The problem is isolated to 1999 to 2001 engines manufactured in Brazil by manufacturer TUPY. Affected engines will have the numbers "53" cast into the engine block on either the passenger or driver side. 1999 to 2001 engines that do not have a "53" designation are less common and manufactured in Mexico by Teskid.

Not all 53 blocks will fail, but there have been some notable cases over the year. Cracked blocks can typically be repaired using the Lock N Stitch method, although it is a burdensome and time consuming repair that requires repeatedly drilling the engine block and installing a series of threaded studs, which are then dressed with a grinding/sanding disc. Welding of the engine is generally ill advised since the large heat input has a tendency to cause additional propagation of the crack and structural welds on cast iron parts requires precise heat control, pre-heating, and post heating in order to create a sound weld. Brazing is another option, but while it can adequately be used to seal the crack the deposited material lacks any strength characteristics that would make it a viable, long term solution.

Improving the performance of your engine via aftermarket upgrades (tuning, fuel system upgrades, etc) is believed to increase the odds that a 53 block will develop a crack, likely due to the difference in engine harmonics. Heavy throttle inputs under load (towing) and failing to let an engine heat up or cool down properly are also believed to contribute to failures. The problem was identified by Cummins and an upgraded casting with reinforced water jackets was prompted, making later engines immune to such concerns.

5.9L Cummins Fuel Pump, Injection Pump, & Injector Failures

1998 to 2007 Cummins equipped Dodge Rams are notorious for lift pump failures, with 1998 to 2004 model years arguably experiencing more frequent failure rates than the later 2005+ trucks due to the location of the lift pump. For 1998 to 2004 model years, the lift pump was located on the engine block adjacent to the fuel filter housing (similar to the location of the mechanical lift pump on 12v engines). For 2005, Dodge relocated the lift pump inside of the fuel tank.

One reason that the earlier pumps are more susceptible to premature failure is they absorb a tremendous amount of heat from the engine block. Another issue with the pump location is that the fuel pump must draw fuel a significant distance from the fuel tank. This large suction head places an excessive strain on the pump and it is not well equipped for this form of fuel transfer (as substantiated by the percentage of early failures). As a result of widespread complaints, Dodge engineers moved the lift pump to inside of the fuel tank and most 2003 to 2004 model year trucks that were sent to dealerships for lift pump repairs received a retrofitted in-tank assembly. While this proved to be a significant improvement, trucks equipped with the in-tank pumps still suffer high lift pump failure rates. While no fuel pump can be expected to last forever, these pumps are somewhat lackluster in their reliability.

While a dead lift pump will leave you stranded, it can be a benign problem that is easily eradicated. On the contrary, it can also become a compounded catastrophe resulting in an expensive repair bill. Without proper fuel flow, the injection pump can quickly become damaged and experience a failure of its own, often littering the fuel system with metallic debris and contaminating the fuel injectors. In such a scenario, the lift pump, injection pump, and fuel injectors need to be replaced in addition to thoroughly cleaning the fuel lines to ensure the replacement injectors do not suffer a similar fate.

Aftermarket lift pump upgrades are largely common amongst Cummins turbodiesel owners as the limitations and shortcomings of the factory setup is well documented. Repairs are particularly expensive on 2003 to 2007 model year trucks as these engines feature the Bosch CP3 injection pump and Piezo electric injectors.

5.9L Cummins Cracked Exhaust Manifolds

Cracked exhaust manifolds are relatively common on 5.9L Cummins turbodiesels as the engines feature an inline cylinder arrangement and thus the manifolds are relatively long. The exhaust manifold expands as its temperature increases and will shrink as it cools when the engine is shutdown. To put it into perspective, a cast iron object 24 inches in length expands roughly 1/16 of an inch when heated from 75° F to 500° F [1]. While 1/16th of an inch does not seem like much, cast iron is a relatively hard material with poor ductility. Take into consideration that the exhaust manifolds may experience intermittent temperatures in excess of 1000° F and it's easy to see that there is a significant amount of expansion and contraction occurring, causing the internal stresses of the manifold to experience cyclic strains in compression and tension. Eventually, the brittle cast iron manifold experiences a failure as a result of these stresses.

Even a small crack in a exhaust manifold can bleed off precious drive pressure in the turbine housing and result in a slight, but noticeable loss of performance. There are many aftermarket exhaust manifold systems on the market that utilize a multi-piece design with slip joints to address movement resulting from expansion and contraction. Exhaust manifold leaks are characterized by a loud, obnoxious knocking or ticking sound from the exhaust manifold that becomes louder and more frequent as engine speed increases. Cracks can propagate and worsen, thus they should be repaired promptly.

[1] - Coefficient of linear expansion assumed 6x10-6 in/in-R

5.9L Cummins ISB Dead Accelerator Pedal

The APPS (accelerator pedal position sensor) on 1998.5 to 2004 model year trucks is renowned for repeated (and often intermittent) failures and reliable concerns. The APPS, which is sometimes mislabeled as the TPS (throttle position sensor), relays the accelerator pedal position to the engine management system. When an APPS fails, it typically causes a "dead pedal" symptom and the engine will not respond to changes in accelerator pedal position. A dead pedal condition is almost always the result of a failed APPS on these model year trucks, and even on some later versions of the 5.9L Cummins. The engine will often, but no always throw one or more DTCs that include P0121, P0122, P0222, and P0223. In less extreme cases, the engine may surge as the APPS signal comes and goes rapidly. Replacement is not particularly difficult, nor is accessing and removing the APPS burdensome. It is, however, somewhat of an expensive part.

5.9L Cummins ECM Failure

ECM failures can be relatively difficult to diagnose and may manifest themselves in the most peculiar of symptoms. Worse yet, ECM failures tend to contribute to intermittent problems and therefore capturing the appropriate PIDs at the time that a problem exists can be difficult, sending technicians on nothing less than a wild goose chase.

The problem with the ECM on 5.9L Cummins engines is its location on the side of the engine block, exposing it to the elements and allowing it to soak up heat produced by the engine. Incidentals that contribute to premature ECM failure include:

• Moisture intrusion, leading to corrosion of the internal ECM circuitry and, in extreme causes, a short circuit condition.

• Faulty wiring and/or a bad sensor causing a short circuit condition.

• A break in the internal circuitry, causing by engine vibration and/or heat exposure.

• Voltage drops or spikes resulting from poor jump start procedures (all electronically controlled vehicles are prone to device failures while jump starting, thus it should be avoided except in emergency situations).

Symptoms of an ECM failure include no start, stalling, and misfire conditions. An intermittent no start only when engine is hot or no start only when engine is cold are also largely common. If a scantool or other OBDII device is unable to connect to the ECM, this is a good sign that the ECM has failed or developed a severe fault. You can expect most conditions to be intermittent as ECM failures do not often occur immediately, but rather develop over a period of time.

6.7L Cummins Clogged DPF (Diesel Particulate Filter)

Chrysler's decision to avoid using diesel exhaust fluid (DEF) may have ultimately backfired, as the early 6.7L Cummins turbodiesels are notorious for DPF clogging. The use of DEF and, more specifically, the selective catalytic reduction (SCR) system allows engines more flexibility in the air-to-fuel ratio range they can operate while meeting Federal emissions regulations. Without DEF, which converts nitrous oxides (NOx) in the exhaust stream, engines must maintain a stricter air-to-fuel ratio that tends to be more on the rich side because diesel engines produce a large amount of nitrous oxides when the A/F ratio is lean. The richer A/F ratio carries less NOx but significantly more particulates, thus diesel particulate filters have a tendency to load quicker and clogged filters become a common occurrence.

Ram Trucks introduced SCR emissions control systems, requiring the use of diesel exhaust fluid, in 2011 for chassis cab trucks and 2013 for pickup trucks. While DPF clogging remains a common problem amongst all modern diesels, the additional flexibility in engine management significantly reduced the volume of trucks experiencing repeated DPF problems and provided significant improvements in fuel economy potential. Cummins and Chrysler were aware of the issue and released multiple re-flashes to attempt to alleviate concerns.

6.7L Cummins Sticking/Stuck Variable Geometry Turbocharger (VGT)

The variable geometry turbocharger forever changed the turbodiesel segment. While products from General Motors and Ford Motor Company began using VGTs in the early 2000's, the introduction of the 6.7L Cummins in 2007 was the first instance of Cummins using a VGT in the Dodge Ram; 5.9L engines all used standard fixed geometry turbochargers. Variable geometry turbochargers utilize a series of mechanisms that alter the geometry of a turbocharger's turbine housing. More constrictive geometry concentrates the exhaust gas stream on the turbine wheel, thus promoting quick spooling with minimal lag. Meanwhile, a more open geometry allows for a viable means of controlling boost without a wastegate and meets airflow requirements on the top end without placing excessive stress on the compressor/turbine wheels and shaft.

The fundamental problem with variable geometry turbochargers is that the moving components in the turbine housing become coated with soot, oil, and/or ash. When the buildup becomes excessive, movement of the VGT mechanism(s) is impeded and turbocharger performance will suffer, generally characterized by excessive turbo lag and/or poor top end engine power.

A sticking, stuck, or clogged VGT typically requires disassembly and manual cleaning in order to restore its function. For 2009, Cummins added an access port to the turbine housing of their Holset turbocharger to aid in cleaning. While this port serves its purpose, removal and disassembly often remains the only solution.

6.7L Cummins Turbocharger Failures

Turbocharger failures are somewhat common on 6.7L Cummins engines, especially on early versions of the engine. For the purpose of this article, a "failure" does not necessarily refer to a turbo that is broken beyond repair, i.e. completely eradicated. Many auto shops will determine that a malfunctioning turbocharger system is a failed turbocharger and simply replace the entire unit, a repair that will typically cost the vehicle owner several thousand dollars, when in fact a more thorough diagnosis may have revealed a much more reasonable repair. A turbocharger failure can include any combination of the following:

• Compromised oil seals allowing engine oil to leak into the compressor and/or turbine housings
• Damaged compressor wheel, typically due to dust/debris infiltration
• Damaged turbine wheel, typically due to excessive heat exposure
• Electronic failures, including the speed sensor and turbo actuator
• Stuck or sticking VGT mechanisms
• Worn bearings, characterized by excessive shaft end play and/or compressor wheel contacting the housing

There's no way around the fact that variable geometry turbochargers are, by design, inherently less reliable that fixed geometry turbos; VGTs are a more sophisticated system with many moving parts. The following considerations may help prolong the life of your turbocharger:

• Check the condition of your air filter frequently and replace as necessary. Air filters are extremely inexpensive, so if you frequently travel in dusty conditions consider replacing the filter often.
• Change your engine oil per the OE recommendations. Engine oil serves as both a lubricant and coolant in turbochargers.
• Routinely use your truck's exhaust brake function. The "exhaust brake" on 6.7L Cummins engines is actually nothing more than an alternative VGT and transmission shift schedule, which constricts exhaust flow by manipulating the position of the VGT mechanism during deceleration. Using the exhaust brake forces the VGT mechanisms to operate frequently in the fully closed position. Exercising these components is believed to help prevent sticking of the mechanisms.
• Allow your engine to idle for 1 to 3 minutes before shutting down the engine, especially after driving for long periods of time under moderate to high load. This allows the turbocharger time to cool; failure to do so allows engine oil to sit and cook in the baking hot turbocharger, degrading the oil and contaminating the turbocharger bearings.
• Identify and repair any problems associated with the turbocharger or emissions system (particularly the EGR system) promptly, as they can contribute to turbo failures. Just because a vehicle still runs "OK" does not mean you should ignore suspected problems.
• Avoid aftermarket power adders such as tuners; they have a tendency to over-work the factory turbocharger. If more power is in your future, invest in a fixed geometry upgrade for the 6.7L Cummins.

6.7L Cummins Head Gasket Failures

Head gasket failures are not particularly common on 5.9L engines, but occur at much higher rates for the 6.7L Cummins. The reason is simple - higher cylinder pressures. The 6.7L Cummins features a much higher factory rating than any of the previous 5.9L models. Achieving high torque output from a relatively small engine requires higher cylinder pressures. While the 6.7's larger bore and stroke contribute greatly to the engine's torque ratings, the fundamentals have not changed; more fuel and air results in greater power.

6.7L Cummins Fuel Dilution

Excessive fuel dilution is an inherent problem on the 6.7L Cummins due primarily to the method in which the engine manages regeneration, the process by which particulate matter captured in the DPF is burned and effectively removed. Rather than utilize a dedicated fuel injector ("7th injector"), the 6.7L Cummins introduces fuel into the exhaust stream by means of a post-injection process while the engine is engaged in active regeneration. The post-injection method releases raw fuel into a cylinder during the exhaust stroke after normal combustion has occurred. The fuel, which is not intended to ignite in the combustion chamber, has a tendency to stick to the cylinder walls where small amounts eventually escape past the cylinder rings and enter the crankcase, contaminating the engine oil.

Fuel dilution is entirely normal and exists in all diesel engines to a certain, acceptable degree. Excessive fuel dilution, however, contaminates the engine oil and reduces the oil viscosity beyond acceptable limits. This theoretically reduces the motor oil's effectiveness as a lubricant and contributes to increased engine wear. Ram Trucks lists 5% fuel dilution as acceptable and suggests owners should have their vehicle diagnosed/serviced if fuel dilution is in excess of this value (source: 2017 Ram 2500/3500/4500/5500 diesel supplement). When fuel dilution is excessive, owners may note that the engine oil level is actually increasing beyond the normal dipstick indicator level. For this reason, and engine is often considered to be "making oil" if it is suffering from excessive fuel dilution.

The following best practices can be used to help reduce the rate of fuel dilution:

• Avoid excessive idling; combustion temperatures decrease significantly when diesel engines are idled for extended periods, and fuel dilution occurs at a higher rate at lower combustion temperatures due to decreased combustion efficiency. Idling periods that are considered "excessive" vary by manufacturer. As a general rule of thumb, we suggest that idling for more than 10 minutes within a 60 minute window is excessive.

• Do not drive a dead cold engine with a load. As previously mentioned, fuel dilution rates are closely related to combustion efficiency. Fuel will have a much higher tendency to stick to the cylinder walls of a cold engine than one that has reached operating temperature. As such, keep the engine load light until the engine has had a chance to warm up.

• If possible, drive a vehicle continuously while it is in active regeneration mode. The active regeneration strategy is significantly more effective while driving at a continuous highway speed than it is idling, and thus the process is likely to complete faster and with a much lower fuel dilution rate.

• Learn your engine and its habits by performing routine oil analyses about 500 to 1000 miles before you require (or expect to require) an oil change. An oil analysis is inexpensive, as are the tools used to extract an oil sample. After several analyses, you should be able to map your fuel dilution rate and construct a service schedule that takes into consideration total fuel dilution.