Black smoke from car exhaust

Black smoke from the exhaust pipe can occur in all types of engines — diesel, gasoline, LPG. If there is black smoke coming from the exhaust, it means that there is a problem with the ignition or an overriched fuel-air mixture.

Therefore, black exhaust, first of all, is a signal of high toxicity of gas, increased fuel consumption and the presence of a problem in the fuel system.

Causes of Black Smoke From Exhaust Pipe

Regardless of what type of engine such trouble has occurred, the common cause in most cases is the same, and it consists of an over-enriched fuel-air mixture being fed in the combustion chamber. It is necessary to consider the specific type of engine because the gasoline one produces black smoke much less than the diesel engine.

Reasons behind emission of black smoke from the exhaust can be related to the problems with the ignition system, the power supply system or the fuel injection system.

What causes black smoke out of exhaust: video

  1. As far as the ignition system is concerned, there are two most common options — a problem with the spark plugs or with the coil(s). If the spark plugs do not give the necessary spark power, then the fuel-air mixture is not fully combusted. In this case, there will be black fouling on the electrodes. In the diesel, there are glow plugs, and if they have the wrong glow, they become the cause of increased smokiness, because then the fuel is not burned.
  2. In the petrol engine, incomplete combustion may be caused by the coil. If it is damaged, ignition skips in separate cylinders are possible. The engine will be unstable and error P0300 — P0306 will be displayed.
  3. In the fuel supply system, problems may be related to the fuel pump and/or fuel injectors. In case of their partial failure, overfueling is possible, as a result of which an enriched fuel-air mixture will be formed.

Why black smoke comes out of the exhaust (gasoline)

Answering the question why there is black smoke from the exhaust pipe of the injector engine, there are two main reasons. The injectors are leaking or the sensors are faulty.

Problems with injectors

Clogged injectors

On the gasoline engine, over time injectors become clogged or covered with deposits. At first there is not enough fuel due to clogged injectors, and then there comes a certain moment when the tightness of the needle valve is violated. Injectors begin to let an excessive amount of fuel into the combustion chamber as well. Naturally, under such conditions the engine will run unstable, jerk, the engine speed will «hunt», especially at idle.

The only way to find out if the injectors are dirty is to check them. In this case it is recommended to clean injectors with a special washer (for example Wynn’s, Liqui Moly or Hi-Gear). Such a procedure should preferably be performed every 50,000 to 60,000 miles of mileage.

Defective sensors

Injector engine operation is based on commands from the electronic control unit (ECU), which in turn receives information from the sensors located in the engine. Therefore, if one of the sensors responsible for the correction of the fuel mixture (oxygen sensor, MAF) works incorrectly, the ECU can give a command to form too enriched mixture, which will lead to black smoke from the exhaust pipe. It does not matter in this case what kind of fuel is used, gas, petrol or diesel. In this case, the black smoke will only be an external sign of malfunction. Also the car will lose its dynamic characteristics, the engine will work with interruptions.

To diagnose the sensors, you can use both a scanner and an ordinary multimeter. When black smoke from exhaust (petrol) occurs at cold start, the first thing to check is the flow/air pressure sensor, engine temperature, throttle, and if on a hot engine, the oxygen sensor (lambda).

Black smoke from diesel exhaust

Diesel black smoke explained: video

There are 4 main reasons for black smoke coming out of the exhaust pipe for any diesel engine:

  • Lack of air (either a clogged air filter or a damaged intake manifold);
  • Low compression;
  • Leaky injectors (especially noticeable at high engine speeds or when driving under load);
  • Disturbed injection torque angle (early angle leads to increased soot formation).

Further about these and other causes in more detail.

Clogged particulate filter

Black smoke from exhaust diesel engines will depend on what environmental standards the car engine meets. Modern environmental standards, in particular «Euro-5», requires the installation of a particulate filter, whose task is to clean the exhaust gas from harmful substances. Accordingly, if it is out of order, there will be black smoke.

With a partially clogged particulate filter, there is black smoke from the exhaust pipe when you accelerate or simply when working in normal mode. There are two ways out of this situation — to replace the particulate filter or to clean it.

High pressure pump failure

HPP failure

In diesel engines, the high pressure pump (HPP) is responsible for supplying and metering the fuel. On diesel engines of the old type (classical) it is enough to check the operation of the pump — its performance, pressure output. In modern diesel engines, in particular, those equipped with the Common Rail system, it is also worth checking the sensors, which provide information to the engine control unit.

Incorrect information from them can also cause black smoke from the exhaust pipe when you suddenly press the accelerator pedal, or just in the normal engine operation mode.

The ignition timing is off

In conventional (conventional) diesel engine systems, the ignition timing can be incorrect, also due to chain stretching. This can cause black smoke from the exhaust when cold, when hot and in other conditions.

In modern Common Rail diesel systems there is no such problem, because the advance angle is set automatically by the engine control unit. If in such a system the angle of advance is straying — it is necessary to check the operability of the electronic control unit itself, as well as the operation of the sensors that affect the correct operation of the engine.

Turbo engines

Engines equipped with turbines have their own nuances. In particular, the turbine can be the cause of black smoke from the exhaust pipe. Under normal operating conditions, the pressure should be higher than the standard atmospheric pressure by 0.8...1 atmosphere. When it malfunctions, when the measured pressure is higher or lower than specified, it can cause black smoke in the exhaust gas.

Fuel filter or inlet line clogging

A fairly common cause of black smoke coming out of the tailpipe is a clogged intake manifold. Most often, the critical element in this case is the air filter. It can be clogged for trivial reasons — it was changed long ago, not according to the current regulations.

Faulty EGR system

EGR contamination

A fairly common reason why there is black smoke coming out of the exhaust pipe is a faulty exhaust gas recirculation system — EGR (Exhaust Gas Recirculation). The matter is that EGR systems are mainly equipped with engines of European cars with moderate climate. But with severe frosts the diesel engine is not heated up as quickly, therefore the sliders and actuators of EGR components are simply clogged with soot. After all, the enriched mixture is fed longer than usual.

Consequently, during normal operation, a lot of the exhaust gas flows back into the intake manifold. This naturally leads to a lack of air for the engine, which in turn leads to black smoke from the exhaust. If the recirculation system is working properly, it closes completely when the engine is fully loaded.

Is it bad if my car blows black smoke?

The first negative thing you will notice is the decrease in engine power with increased fuel consumption, but if you are wondering what the consequences of black smoke from the exhaust pipe are, and if you can drive a car with this symptom at all, there are 3 main caveats to note:

  • Load on the catalytic converter (particulate filter);
  • burnout of pistons and valves (the whole cylinder block is under attack as extra fuel gets into oil, scuffing occurs);
  • valve malfunction (hanging up because of carbon deposits).
If you can smell a distinct smell of fuel after taking out the dipstick and the grease became visibly greasier — you need to urgently search for the cause otherwise you will face a rapid deterioration of the cylinder-piston group.

Have you ever complained of black smoke coming out of the exhaust pipe? What do you think about it? Share your opinion in the comments.


  • What causes black smoke in exhaust?

    The main reason of black smoke is exhaust — your car is burning too much fuel. It can be caused by: failed fuel injection system, clogged air filter or clogged manifold.

  • Can I Drive My Car with Black Smoke?

    Yes, you can. But to prevent more serious damages and decrease fuel consumption, we recommend to fix the problem as fast as you can.

  • How to fix black smoke from exhaust?

    Fixing the black smoke from exhaust needs several steps to be done: 1) Air system cleaning; 2) Pouring a special fuel additives; 3) Check the engine rings and replace if they are damaged.

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