How to diagnose common diesel engine problems?

Diagnosing diesel engines on heavy vehicles requires a systematic approach:

Common problems and diagnostics:

• Hard starting: Check the glow plugs — they must reach 800-1,000 °C. Test with a multimeter: normal resistance 0.5 to 2 Ω. Also check fuel pressure (min 30 PSI for common rail engines)
• Power loss: Check the fuel filter (change every 15,000-30,000 km), the turbocharger (max axial play 0.5 mm), and the EGR valve — EGR clogging is a frequent cause
• Excessive smoke: Black smoke = too much fuel (injectors, timing), blue = oil (rings, valve seals), white = coolant (head gasket) or unburned diesel
• Abnormal noise: Metallic knocking may indicate a faulty injector or valve clearance issue

Using a diagnostic scanner (J1939/CAN bus) is essential to read error codes (DTC) on modern engines. Professional scanners cost $1,000 to $5,000.