Excessive Black Smoke from Diesel Engine – Causes & Fixes

Reducing Excessive Black Smoke from Diesel Engine

Some people perceive Diesel engines to be loud and dirty but did you know that although black smoke is quite common with these types of engines it shouldn’t be so?

That notwithstanding, if your diesel engine is expelling black smoke you shouldn’t be overly worried as it can be easily handled.

Causes of Black Smoke from Diesel Engine

  • Accumulated Carbon Buildup
  • Clogged Air Filter
  • Faulty fuel system
  • Faulty MAF Sensor


We will be taking a look at the various ways by which black smoke occurrence can be reduced.

How to Reduce Black Smoke from Diesel Engine / Exhaust When Accelerating

1. Incorporate Diesel Additive to your diesel

If your car is an old one or it has racked up a lot of miles, then the problem might be as a result of accumulated carbon buildup. If that is the case, using a diesel additive can really help to clean the carbon buildup and handle the issue of black smoke from your engine.

You should make your research and be sure that the diesel additive that you are going for is one that is of very good quality.

Does Diesel Additive work

Apart from taking care of the problem of black smoke from your engine, there are other things that diesel additives can help with. There are various fuel additives with unique properties available in the market that you can choose from, depending on what you need.

For instance, you can pick a fuel additive to help you have a cleaner engine, or one to stabilize the fuel before winter.

Note however, that diesel additives are not the solution to all of your engine problems.

How much is Diesel Additive

A bottle of diesel additive normally goes for less than $15 a bottle. Be sure to go through the directions for use so as to know the rate at which you should use it.

Using a diesel additive is not hard at all, all you have to do is pour it into your fuel tank when you fill up and you are good to go. Assuming the diesel additive you added is to help you with the issue of black smoke, you should start seeing results.

2. Replace the Air Filter

If you observe that your diesel engine is giving out black smoke you should take a look at your air filter. If after you have checked your air filter, you discover that it is dirty then you will have to change it.

When you have black smoke being expelled from your engine, it is a pointer to the fact that fuel is not properly burned in the combustion chamber.

It means that there is something hindering the complete combustion of the fuel and this would usually be as a result of a wrong ratio of the air-fuel mixture.

You have to check the air mixture that goes into the combustion chamber. If the air filter is clogged, that will mean that there is not enough air getting into the engine.

This will cause the air/fuel mixture to run rich and result in the incomplete combustion of the diesel fuel. If that is the case, then you have to replace the engine air filter.

Signs of a Clogged Air Filter

Apart from the black smoke that is being expelled from your diesel engine, there are other symptoms that are indicative of a clogged air filter.

Remember that a clogged air filter can cause an imbalanced air/fuel mixture and this can result in a loss of power when you are exerting too much pressure on the engine or while accelerating.

You might also observe that your engine is consuming more fuel than normal and this would occur as a result of the fact that your engine is not at its optimum.

Cost of changing Air Filter

It will do you much good if you include replacing your air filter as part of your scheduled maintenance. Although a lot of car manufacturers will suggest that it should be replaced every 12,000 to 15,000 miles, you can still go through your owner’s manual to know the recommendation of your automaker on the subject.

You can get an air filter for about $10 to $75. It doesn’t take time to install and you can even do it by yourself, but if you feel you won’t be able to, it is best that you contact a professional to help you out with it.

3. Check the Fuel System

It is recommended that you inspect your fuel system to see if the issue is coming from any of the parts. You can take a look at EGR system or fuel filter as sometimes it could just be that you have a faulty EGR valve or fuel filter and once you change them, that solves the problem. You should also check to see if you need to change your fuel injector cleaner.

To get more information check the trouble codes using an OBD2 scanner. This should tell you whether or not there is an issue with your fuel system.

Signs of a faulty fuel system

In a situation where your diesel engine is receiving an erroneous amount of fuel, the after math could be black smoke being expelled from your exhaust. You might also observe that you have a rough idle.

Another likely symptom is that your engine will use up fuel more than normal. Sometimes if the fuel is not burned properly, you can even perceive it.

Cost of fixing Diesel Fuel System

If after you have conducted the appropriate checks and you find out that what you need to do is to replace the fuel filter, which will cost you about $50 to $100. In fact, it is advised that you replace your fuel filter regularly, between 10,000 to 25,000 miles for optimum performance.

But be sure to take the type of filter as well as the automaker’s recommendations into consideration.

On the other hand, if what you have to change is maybe your diesel injection pump then you are going to spend much more as this will cost you about $1,700 and $2,400 for parts and labor.

4. Clean out or change the MAF Sensor

The mass airflow sensor sees to it that the appropriate quantity of fuel mixes up with the air coming into the combustion chamber. So if the MAF Sensor should malfunction it disrupts the air-fuel ratio.

This is because it misinterprets the amount of airflow coming into the system leading to the wrong amount of fuel being added. This can result in various issues one of them being black smoke due to unburned fuel.

Sometimes, all that is required to take care of this issue is to clean the MAF sensor. This can be done using an electronic cleaner and you have to be really careful while doing this, so as not to damage the sensor.

Signs of a faulty MAF Sensor

Usually, your Check Engine Light should come on if your MAF sensor becomes faulty. Using your OBDII scanner you can read the trouble codes and ascertain the issue.

Another way you can also become aware of this problem is if you observe that there is black smoke being expelled from your exhaust. If you are also finding it difficult to accelerate, that could be a pointer to an issue with your MAF sensor.

Other symptoms of a faulty MAF Sensor include hard starting, rough idle, as well as poor fuel economy.

You have to check out the MAF sensor to be sure that is really the cause of the symptoms you are noticing with your vehicle.

Cost of changing MAF Sensor

Changing the MAF sensor can cost you about $220 to $350. While the cost of parts is about $175 to $280, you will spend about $45 to $70 on labour.

If you know how to, you can carry out the replacement by yourself and save the amount you would have spent on labour. But if you are not sure that you can replace it yourself, contact a professional.


Please enter your comment!
Please enter your name here