Diesel
8 LessonsDiesel engine operation, common rail injection, DPF, DEF, and diesel-specific diagnostics.
Overview
Diesel engines dominate commercial vehicles and heavy-duty trucks. This module covers compression ignition, common rail fuel systems, turbocharging (nearly universal on modern diesels), diesel particulate filters (DPF), diesel exhaust fluid (DEF/SCR), and glow plug systems.
Key Components
- High-pressure common rail fuel system
- Variable geometry turbocharger (VGT)
- Diesel Particulate Filter (DPF)
- SCR system and DEF injection
- Glow plug system
- EGR cooler
How It Works
Diesel engines use compression ignition — fuel is injected into highly compressed, superheated air and ignites without a spark. Common rail systems pressurize fuel to 25,000+ PSI for precise injection control. The DPF traps soot particles and periodically burns them off (regeneration). The SCR system injects DEF to reduce NOx emissions.
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Join the Nation — FreeCommon Problems
- DPF soot loading from too much idle time
- DEF quality issues causing SCR codes
- Injector failure from water in fuel
- EGR cooler leaks
- Glow plug failure causing hard cold starts
Diagnostic Tips
- Fuel rail pressure is the first thing to check on performance complaints
- DPF soot level and regen history in scan data
- Check DEF quality with refractometer
- Diesel injector return flow test identifies weak injectors
Related Systems
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