Improving Your Automobile

Don't Choke On Smoke: Diagnosing Causes Of Black Smoke In Diesel Engines

20 September 2016

Addison Morris

Black smoke emanating from your vehicle's exhaust system is never a welcome sight, but it's one that may be all too familiar to owners of malfunctioning diesel engines. Unfortunately, there is no single clear-cut cause of this worrying symptom of engine trouble. Here are some of the most common causes of black smoke, along with ways the cause of the problem can be repaired:

Over-fuelling

Probably the most common cause of black smoke spewing from diesel engines, over-fuelling occurs when too much fuel and, by extension, not enough air is allowed into the cylinders of your engine. This causes diesel to burn incompletely, creating clouds of black smoke laden with airborne particles of unburnt fuel. There are a number of reasons why your cylinders may be taking in too much fuel:

• Faulty or aged fuel injectors (pay particular attention to wear around the injector needles, as this can reduce the injector's ability to regulate fuel dosage)
• Faulty or mistimed fuel injector pumps
• Faulty or clogged EGR (exhaust gas recirculation) valves
• Faulty or clogged turbochargers in turbo-diesel engines
• Poorly adjusted valve clearances

If you suspect over-fuelling is causing your diesel engine to create black smoke, you should have service personnel trained in diesel repairs inspect these various components for wear and damage as your first priority.

Clogged air filters

Even if your engine's cylinders are taking in the correct amount of fuel, they may not be taking in enough air to burn the diesel effectively. One of the chief causes of insufficient air is clogged air filters -- these devices filter out contaminants and particulate matter from the air used to burn diesel and need to be changed regularly as they become clogged with detritus. Clogged filters can also noticeably reduce engine power and may pose a fire hazard in cases of extreme neglect.

If this problem is the source of your black smoke, the solution is relatively simple: Simply clean your air filters with a suitable air filter cleaning solution (preferably made by the manufacturer of your vehicle, although many third-party options are safe and effective), or swap them with new ones if they have reached the end of their usable life.

Burning oil

Sufficient levels of uncontaminated engine oil are vital for the smooth operation of any diesel engine, but if allowed into the fuel cylinders in excessive quantities, it can burn, another potential cause for black smoke. Worn oil valves commonly cause this problem, as do worn or perished stem seals and cylinder liners, so make sure to have these parts thoroughly inspected if you suspect your engine is burning excessive oil. You should also pay attention to the type of engine oil you are using in your diesel engine as unsuitable or contaminated oils can chemically react with internal components and cause wear and corrosion.

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