We can generally understand what is wrong with a diesel engine by the colour of smoke emitted from the exhaust. There are three basic colours – black, white and blue.
Black Smoke
This is due to an air to fuel ratio imbalance, either the fuel system is delivering too much fuel into the engine or there is not enough clean air (oxygen ) a few things to look for:
- Faulty injectors (injectors need attention at about 100.000 to 120 000 miles) check for injector blow-by.
- Faulty injector pump, this is more relevant to pre common rail systems.
- A dirty air cleaner or restricted air inlet, check swirl flaps if applicable.
- Turbocharger or intercooler faulty
- Problems within the cylinder head, valves clogged up due to faulty EGR (exhaust gas recycling unit)
- Engine timing problems, check cam to crank timing.
White Smoke
Normally means that the fuel injected into the cylinder is not burning correctly. The smoke will burn your eyes.
- Engine/pump timing out
- Fuel starvation to the pump causing the timing of the pump not to operate correctly
- Low engine compression
- Water/petrol in the fuel
- Injectors dribbling.
Blue Smoke
- The engine is burning engine oil
- Worn cylinders or piston rings
- Faulty valves or valve stem seals
- Engine over full with engine oil
- Faulty injector pump/lift pump allowing engine oil to be mixed with the diesel
