If the exhaust smoke is black

• Black smoke from the exhaust indicates that the fuel combustion is unbalanced. This means that there is too much fuel in relation to the air with which it is mixed inside the combustion chamber. Explanation: either there is not enough air, or there is an excessive amount of fuel.

• If your vehicle has fuel injection, it may be that the sensors of the injection system are not well-situated. If any one of the sensors are malfunctioning or not well-situated, it’s possible that too much fuel is being injected into the cylinder, creating too rich of a fuel mixture, resulting in unbalanced combustion and therefore black smoke. In this case, you must bring your vehicle to a garage to have the injection system checked out and any faulty sensors replaced.

• It may also be that the air filter needs to be changed. A dirty air filter prevents sufficient levels of air, and will consequently cause the air/fuel mixture to be too rich in fuel. Fuel consumption is therefore unbalanced and black smoke in the exhaust will occur.

If the color of the smoke is blue

• Blue smoke is a very bad indicator that oil is burning in your engine. Take your vehicle in to be inspected as soon as possible to determine the source of the leak.

• If you used a low-quality oil for your last oil change, the oil must be changed as it is either too viscous or too diluted. In such cases, the oil is escaping through the seals and into the combustion chamber where it burns and produces a blue smoke.
• If your vehicle is old or if it has been driven excessively, it’s possible that the engine has become worn, resulting in internal oil leaks. In this case, it is necessary perform an engine overhaul.
• If your car lacks power, particularly when going up hills, it’s possible that the piston segments are defective. If it’s indeed the case, oil can get into the combustion chamber and burn, resulting in blue smoke. Faulty segments will result in decreased power, necessitating a costly replacement of the parts.

• If the vehicle has normal power, and the smoke emits mainly during acceleration, this is a valve stem leak. In this case, it is necessary to replace the valves.
• Finally, if you have a turbo engine, it is possible that the source of the leak is in the turbocharger. Oil escapes through his leak into the exhaust system and burns in the form of blue smoke.

If the color of the smoke is white

• White smoke results from the condensation of hot water vapor coming into contact with the cold outside air.

• If white smoke emits when you first start a cold car in cool weather, it’s perfectly normal. This is simply the result of the evaporation of the water that has accumulated inside the exhaust system while the car was stationary. Rest assured, all is well!
• If you see white smoke coming out of the exhaust all the time, even when the engine is hot, this is due to a leak in the head gasket. If the gasket is cracked or worn, water will penetrate into the cylinders, and, under the effect of elevated temperature, will create white smoke that is emitted out the exhaust system. When this occurs, you must first check the coolant level of your vehicle. If low, it’s a bad sign and it is then imperative to see a mechanic as soon as possible.

Smoke standards according to vehicle emissions
 
To be completed four years after the purchase date of a new vehicle, and every two years thereafter, vehicle inspections are imposed to ensure that the vehicle is safe and within the limits of pollution standards.
 
During the inspection, emissions are tested to verify that air pollutants are below the threshold as set by the regional anti-pollution standards. In the event that a vehicle does not pass emissions testing, it must undergo the necessary modifications to fall back under compliance and be re-tested in order to determine if it is roadworthy or not.

Emission standards for gas engines

​For cars running on gasoline, carbon monoxide (CO) emissions must be less than

• 4.5% for engines built between 1972 (the year in which the first anti-pollution standards went into effect) and September 1986.
• 3.5% for engines built between October 1986 and 1993 (1995 if without a catalytic converter).
• 0.5% at idle and 0.3% at 2,500 revolutions/minute for engines built between 1996 and July 2002 for vehicles without integrated anti-pollution equipment, and between 1994 and 1995 for vehicles with integrated anti-pollution equipment.
• 0.3% at idle and 0.2% at 2,500 revolutions/minute for engines built after 2002.

Anti-pollution standards for diesel engines

For cars running on diesel, opacity levels of exhaust fumes should be less than:

• 3 M-1 for turbo engines.
• 2.5 M-1 for cars built until mid-2008 without turbo engines.
• 1.5 M-1 for cars built after mid-2008 without turbo engines.

 
Gas vehicles manufactured prior to 1972, and for diesel vehicles manufactured prior to 1980 -- that is to say, before pollution standards went into effect -- are exempt from emissions control.
 
Finally, although engine noise is measured, it will not lead to a re-test if deemed excessive.

How to limit the emission of smoke in order to pass emissions testing?

The least expensive option, with no need for disassembly and entailing the shortest service time, and which is an alternative to part replacement, is hydrogen treatment via the Carbon Cleaning station. This service works as a preventative treatment, recommended every 10,000 miles, but can also resolve existing problems in the engine. This operation costs only $155.