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Diesel smoke

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Diesel smoke?

Faulty or worn diesel injectors

You can see if a diesel engine is running properly by the colour of the exhaust smoke. Diesel smoke tells all. 

Excessive smokediesel injectors

Most often you’ll see black smoke when something is wrong 

White smoke or blue smoke is also possible. 

We’ll cover all three types here.

Excessive smoke is a symptom of a poorly diesel engine
Black smoke means either too much fuel or not enough air.
The balance of air and fuel must be correct; so if the engine is overfuelling you’ll get black smoke.
If the engine is short of air, perhaps a blocked or dirty air filter you’ll also get black smoke.




EGR (exhaust gas recycling) valves can cause problems on some engines.
Check to make sure the valve is not jammed

Check list – check these suspects to find the cause of the problem.

Faulty diesel injector/s

fuel pressure low       faulty fuel pressure sensor or valve

Faulty high pressure pump
Air intake/filter restricted or blocked

injector seating washer leaking (blow-by)
cam/crank sensor


White smoke means unburnt fuel.white smoke

Fuel injected into the engine is not being burnt completely.

Compression is very important in a diesel engine.

When diesel fuel is injected into hot compressed air it ignites;

low compression will result in poor running.

It’s easy to put petrol in the tank by mistake.

Contamination like this will result in unburnt fuel and white smoke!

White smoke check these:            compression – is it low?

fuel quality is there water or petrol contamination?

pump timing – is fuel being injected at the right time?
valve seat wear


Blue smoke indicates engine lubricating oil being burnt.
Check list:
cylinder bore wear,
piston ring wear,
valve stems/seals worn
Engine oil from the sump is getting into the combustion chamber and being burnt