Manufacturer Expertise
Ram Cummins diagnostics, repair & maintenance
STL Diesel works on diesel trucks in Crystal City, Missouri and serves owners and fleets throughout Festus, Herculaneum, Pevely, Hillsboro, De Soto, Jefferson County and the southern St. Louis region.
Our process starts with the customer concern, a vehicle inspection and scan data, followed by system-specific testing. We diagnose before recommending parts so the repair plan is based on test results rather than guessing.
Book an AppointmentEngines & generations we support
- 5.9L Cummins
- 6.7L Cummins
- 2019+ 6.7L Cummins applications
Call 636-465-0585 with your year, model, engine and symptoms.
Common Concerns
What we diagnose on Ram Cummins trucks
Fuel pressure & injector concerns
Lift-pump supply, filtration, rail pressure, injector return and high-pressure pump performance are considered together when diagnosing hard starts or low power.
Turbo & boost control
Boost leaks, VGT control, actuator faults, exhaust restrictions and fueling concerns can overlap and require data-driven diagnosis.
2019+ valvetrain concerns
Ticking, misfire, metal debris or valvetrain symptoms on later 6.7L applications should be investigated promptly to limit additional damage if a mechanical failure is present.
DPF, DEF & SCR warnings
Frequent regeneration, DEF warnings and emissions faults can come from sensors, dosing, soot load, exhaust leaks or an engine problem that increases soot or NOx.
Cooling & engine concerns
Overheating, coolant loss, blow-by, oil-pressure complaints and internal engine noises are diagnosed with appropriate mechanical and electronic tests.
68RFE / drivetrain concerns
Shift complaints, heat, slipping and driveline issues are evaluated with transmission data, fluid condition and the truck’s power and towing use in mind.
How STL Diesel Diagnoses
A test-first repair process
- Confirm the concern. We start with the symptoms, operating conditions, history and stored fault codes.
- Check data and basics. We compare commanded and actual values and inspect the mechanical, electrical, air, fuel and cooling systems involved.
- Perform pinpoint tests. Pressure, leak, electrical, contribution, temperature or other tests are used as appropriate.
- Explain the findings. You receive the test results and repair priorities before work moves forward.
- Verify the repair. The system is rechecked after repair to confirm the original problem is corrected.
Quick Answers
Ram Cummins repair FAQ
What Cummins engines does STL Diesel work on?
STL Diesel services 5.9L and 6.7L Cummins trucks, including later-model Ram applications.
What are warning signs of a 2019+ 6.7 Cummins valvetrain problem?
New ticking or knocking, rough running, misfire symptoms, abnormal metal in the oil or filter, and performance changes deserve prompt inspection. The exact cause must be confirmed before deciding on a repair.
Why does a Cummins keep regenerating?
Short trips, excessive idling, low exhaust temperature, boost or fueling problems, sensor faults and DPF restriction can all increase regeneration frequency. The cause should be diagnosed rather than repeatedly forcing a regen.
Need help with your Ram Cummins?
Call STL Diesel at 636-465-0585 or schedule an appointment in Crystal City, Missouri.
Book Appointment