The 6.7L Cummins engine is widely known for its power, reliability, and longevity. Found in many Ram heavy-duty trucks since 2007, this diesel workhorse has proven itself in countless demanding environments. However, like all engines, it's not without its issues. Whether you're a fleet manager, diesel mechanic, or DIY truck enthusiast, understanding the most common problems with the 6.7L Cummins can help you detect issues early and avoid costly repairs.

In this article, we’ll break down the most common problems associated with the 6.7L Cummins engine and provide insights on causes, symptoms, and potential solutions.

1. EGR System Failure (Exhaust Gas Recirculation)

Issue:

One of the most frequently reported problems is the EGR valve and cooler clogging with carbon deposits. Over time, soot buildup can restrict airflow and reduce performance.

Symptoms:

  • Poor fuel economy

  • Engine knocking

  • Loss of power

  • Check engine light (CEL)

Solution:

Regular EGR cleaning, or for off-road or performance builds, EGR delete kits (where legal). Also consider high-quality fuel and oil to reduce carbon buildup.

2. DPF Clogging (Diesel Particulate Filter)

Issue:

The DPF is part of the emissions system and designed to trap soot from the exhaust. However, it often clogs, especially under low-speed or city driving conditions.

Symptoms:

  • Regeneration cycle happening too often

  • Excessive smoke

  • Decreased engine performance

  • Limp mode activation

Solution:

Use of high-quality diesel fuel, regular long drives to trigger passive regeneration, or DPF replacement/cleaning. Tuning or DPF delete options may be used in off-road applications.

3. Turbocharger Problems

Issue:

The Holset turbocharger in the 6.7L Cummins is known to develop issues, particularly with the variable geometry turbo (VGT) system. The actuator can fail due to heat and carbon buildup.

Symptoms:

  • Loss of boost pressure

  • Engine hesitation

  • CEL with turbocharger-related codes

  • Whining or unusual noises

Solution:

Routine inspection and cleaning. Replace the actuator or the entire turbo unit if necessary.

4. Head Gasket Failure

Issue:

Although not extremely common, some owners experience head gasket failure due to high boost pressure or prolonged overheating.

Symptoms:

  • White smoke from exhaust

  • Coolant loss with no visible leaks

  • Bubbles in radiator/overflow tank

  • Engine overheating

Solution:

Install head studs and a new head gasket—especially important if you are tuning for more power. Maintain proper cooling system health.

5. Fuel System Issues (High-Pressure Pump & Injectors)

Issue:

The CP3 and later CP4 injection pumps can be prone to failure. CP4, in particular, has a reputation for internal failure which can contaminate the entire fuel system.

Symptoms:

  • Hard starting

  • Rough idle

  • Engine stalling

  • Metal shavings in fuel system

Solution:

Upgrade to a CP3 conversion kit (replacing CP4). Use high-quality fuel and install a lift pump to improve filtration and fuel pressure stability.

6. Crankcase Ventilation System Problems

Issue:

The crankcase ventilation filter (CCV) can clog over time, leading to increased pressure and potential oil leaks.

Symptoms:

  • Excessive oil consumption

  • Leaks around valve cover or front cover

  • High crankcase pressure

Solution:

Replace the CCV filter every 60,000–70,000 miles or as needed. Consider a CCV delete kit in non-road-legal builds.

7. Transmission Mating & Torque Management Issues

Issue:

While not part of the engine itself, the transmission mated to the 6.7L Cummins—especially the 68RFE—often becomes a weak link, unable to handle increased torque.

Symptoms:

  • Slipping gears

  • Harsh shifting

  • Transmission overheating

  • CEL with transmission codes

Solution:

Upgrade the torque converter and valve body, or swap to a more robust transmission such as the Aisin AS69RC or a built 48RE for performance applications.

Conclusion: Keeping Your 6.7L Cummins Healthy

Despite these issues, the 6.7L Cummins remains a solid and reliable engine, especially when properly maintained. Regular servicing, the use of high-quality parts and fluids, and early diagnosis of problems can significantly extend its lifespan.

If you’re running a fleet or rely on your Ram truck for work, it’s crucial to stay ahead of these common issues. And when replacement parts are needed—whether it's a turbo actuator, head gasket kit, or a complete fuel system upgrade—be sure to source them from a trusted supplier that specializes in Cummins parts.