Introduction

The Cummins C Series engines (6C, 6CT, 6CTA) are engineered to deliver high performance while meeting stringent emission regulations. With evolving environmental standards between 1991 and 1994, Cummins integrated advanced emission control systems to reduce harmful pollutants, including Nitrogen Oxides (NOx), Particulate Matter (PM), Carbon Monoxide (CO), and Unburned Hydrocarbons (HC).

Parts Catalog for Cummins 6C Marine Engine
Parts Catalog for Cummins 6CT Marine Engine
Parts Catalog for Cummins 6CTA Marine Engine
Parts Catalog for Cummins ISC Marine Engine
Parts Catalog for Cummins QSC Marine Engine

This guide provides an in-depth exploration of:

1. Components of the Emission Control System
2. Servicing Emission-Related Parts for Compliance
3. Common Issues and Solutions

By understanding these systems, operators can maintain compliance, optimize engine efficiency, and extend the life of their engines.

1. Components of the Emission Control System

A. Exhaust Gas Recirculation (EGR) System

The EGR system is critical for reducing NOx emissions. It recirculates a portion of the engine’s exhaust gas back into the intake manifold, lowering combustion temperatures and, consequently, NOx production.

• Key Components:
  

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  • EGR Valve: Controls the flow of exhaust gases into the intake.
  • EGR Cooler: Lowers the temperature of recirculated exhaust gases to improve efficiency.
  • EGR Control Solenoid: Manages valve operation based on engine load and temperature.
    

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1991 vs. 1994 Differences:

• 1991 engines used basic mechanical EGR valves.
• 1994 engines introduced electronically controlled EGR systems, offering precise management for better emissions control.
  

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B. Diesel Oxidation Catalyst (DOC)

The DOC reduces CO and HC emissions by oxidizing them into less harmful substances like CO₂ and H₂O.

• Components:
  • Catalyst Core: Coated with precious metals (platinum or palladium) to facilitate chemical reactions.
  • Substrate: Ceramic or metallic honeycomb structure to maximize surface area.
    

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Note: DOC systems became more prevalent in post-1994 engines due to stricter regulations.

C. Particulate Filter (DPF)

Though not standard on 1991 or 1994 models, DPFs were introduced later to capture soot particles from diesel exhaust.

• Key Components:
  • Filter Element: Traps PM and allows clean gases to pass through.
  • Regeneration System: Burns off accumulated soot during high-temperature cycles.
    

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D. Turbocharger with Aftercooler

The turbocharger not only boosts engine power but also improves emissions by enhancing air-fuel mixing. The aftercooler reduces intake air temperature, lowering combustion temperatures and NOx production.

• Components:
  

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  • Compressor & Turbine: Increases intake air pressure.
  • Aftercooler: Reduces intake air temperature for better combustion control.
    

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E. Fuel Injection System

Advanced fuel systems directly influence emissions by optimizing injection timing, pressure, and fuel atomization.

• 1991 Engines: Primarily mechanical fuel injection systems.
• 1994 Engines: Adopted electronic fuel injection (EFI) for precise control, improving combustion efficiency and reducing emissions.
  

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2. Servicing Emission-Related Parts for Compliance

Proper maintenance of emission control components is essential to ensure compliance with regulatory standards and to maintain engine efficiency.

A. EGR System Maintenance

1. EGR Valve Cleaning:
   

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   • Symptoms of Failure: Rough idling, increased NOx emissions, reduced fuel efficiency.
     

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   • Service Steps:

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       Remove the EGR valve.

     • Clean carbon deposits using an approved solvent.
     • Inspect the valve for sticking or damage.
       

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2. EGR Cooler Inspection:
   

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   • Check for clogging and internal leaks (coolant contamination).
   • Flush with a cleaning solution if clogged.
     

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3. EGR Solenoid Check:
   

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   • Use a multimeter to verify electrical continuity.
   • Replace faulty solenoids to ensure proper valve operation.
     

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B. Diesel Oxidation Catalyst (DOC) Service

1. Visual Inspection:
   

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   • Check for physical damage or blockages.
   • Lookfor signs of soot buildup or melting, indicating overheating.
     

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2. Cleaning Procedure:
   

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   • Use compressed air to remove loose soot.
   • For severe clogging, professional cleaning with specialized equipment is recommended.
     

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3. Replacement Criteria:
   

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   • If performance issues persist after cleaning, consider replacing the DOC.
     

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C. Fuel Injection System Maintenance

1. Injector Cleaning:
   • Symptoms of dirty injectors include misfires, black smoke, and reduced power.
   • Use diesel injector cleaner additives or remove injectors for ultrasonic cleaning.
     

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2. Checking Injection Timing (1991 Mechanical Systems):
   

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   • Verify timing with a dial indicator.
   • Adjust as necessary for optimal combustion.
     

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3. Electronic Fuel Injector Testing (1994 Systems):
   

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   • Use a diagnostic scanner to check for fault codes.
   • Test injector response times and fuel delivery rates.
     

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D. Turbocharger and Aftercooler Service

1. Turbocharger Inspection:
   

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   • Check for shaft play, oil leaks, and damaged blades.
   • Clean the compressor housing if carbon buildup is present.
     

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2. Aftercooler Maintenance:
   

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   • Inspect for oil contamination (may indicate turbo seal failure).
   • Clean using a mild detergent and ensure there are no leaks.
     

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3. Common Issues and Solutions

Emission systems can develop issues over time due to wear, carbon buildup, or sensor failures. Early diagnosis and corrective action prevent costly repairs.

A. Excessive NOx Emissions

• Causes:
  

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  • Faulty or clogged EGR valve.
  • Incorrect fuel injection timing.
  • Overheating due to poor cooling system performance.
    

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• Solutions:
  

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  • Clean or replace the EGR valve.
  • Verify and adjust injection timing.
  • Inspect the cooling system for blockages.
    

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B. Increased Particulate Matter (PM) Emissions

• Causes:
  

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  • Dirty air filters reducing oxygen supply.
  • Worn fuel injectors causing poor atomization.
  • Turbocharger inefficiency.
    

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• Solutions:
  

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  • Replace air filters regularly.
  • Clean or replace fuel injectors.
  • Service the turbocharger to restore proper airflow.
    

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C. Poor Fuel Economy

• Causes:
  

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  • Faulty sensors (e.g., MAP, MAF) providing incorrect data.
  • Clogged fuel filters affecting fuel delivery.
  • Exhaust restrictions from a damaged DOC.
    

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• Solutions:
  

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  • Test and replace faulty sensors.
  • Change fuel filters as part of routine maintenance.
  • Inspect the exhaust system for blockages.
    

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D. Rough Idling or Engine Hesitation

• Causes:
  

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  • EGR valve stuck open, causing unstable combustion.
  • Air leaks in the intake system.
  • Malfunctioning fuel injectors.
    

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• Solutions:
  

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  • Clean or replace the EGR valve.
  • Check for loose or damaged intake hoses.
  • Service or replace injectors as needed.
    

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E. Fault Codes and Diagnostic Troubleshooting

Using Diagnostic Tools:

1. OBD Scanner (1994 Engines):
   

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   • Connect to the diagnostic port to retrieve trouble codes.
   • Interpret codes using Cummins documentation.
     

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2. Live Data Monitoring:
   

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   • Monitor sensor readings in real-time to identify anomalies.
     

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3. Smoke Testing:
   

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   • Check for intake or exhaust leaks that affect emissions.
     

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Proactive Tips for Emission System Longevity

1. Use High-Quality Diesel Fuel:
   

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   Prevents injector clogging and reduces carbon buildup.

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2. Regular Maintenance Schedule:
   

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   Follow Cummins’ recommended intervals for EGR cleaning, filter changes, and fuel system service.

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3. Monitor Engine Performance:
   

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   Unusual smoke, reduced power, or poor fuel economy often indicate early emission system issues.

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4. Keep the Cooling System in Top Shape:
   

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   Overheating affects EGR performance and increases NOx emissions.

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5. Avoid Short Trips:
   

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   Engines running below optimal temperature produce more carbon buildup, affecting EGR and DOC systems.

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Conclusion

Proper maintenance of emission control systems in Cummins C Series engines is essential for regulatory compliance, fuel efficiency, and engine performance. Understanding the role of each component, conducting regular inspections, and addressing issues promptly ensures your engine operates cleanly and efficiently.

Whether managing 1991-certified engines with basic mechanical systems or 1994-certified models with advanced electronic controls, proactive maintenance is the key to longevity and reduced emissions.

Parts Catalog for Cummins 6C Marine Engine
Parts Catalog for Cummins 6CT Marine Engine
Parts Catalog for Cummins 6CTA Marine Engine
Parts Catalog for Cummins ISC Marine Engine
Parts Catalog for Cummins QSC Marine Engine

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