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What Causes Engine Knocking? Six Important Causes!

Symptoms of engine tapping

Understanding what causes engine knocking can be extremely helpful to prevent the problem from occurring in the first place. Typically, engine knocking happens due to one of the following reasons:

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  1. Low-quality fuel
  2. Bad ignition timing
  3. Wrong air-fuel mixture
  4. Faulty knock sensor
  5. Damaged bearing
  6. Malfunctioning belt and tensioner

The more we drive our cars, the more we can detect any new weird noises. Experts recommend taking these noises very seriously because they might be linked to major internal problems that could be resolved without major repair costs.

Engine knocking is that type of problem that indicates a serious issue. Simple tips can resolve it, but they might require major replacements that cost thousands of dollars on repairs. However, understanding what causes engine knocking can help you prevent the problem from occurring in the first place.

This article provides you with all you need to know about what causes engine knocking. It specifically highlights six very common causes that could lead to engine troubles, including engine knocking. It also provides you with a general overview of the whole concept of engine knocking and how it occurs to understand better how complicated and how serious the problem is.

What is engine knocking, and how does it sound like?

While it's very important to understand what causes engine knocking, it is as important to understand what engine knocking is in the first place and how it occurs and what it could lead to.

The best way to understand the complexity of engine knocking is to go back to the basics and understand how the combustion process happens. Typically, your engine's cylinder will suck a specific amount of air and fuel to get them mixed, and then it compresses them by raising the piston ring upwards. Once the air-fuel mixture reaches a specific pressure and temperature threshold, the sparkplug sends a spark to ignite the mixture and smoothly causes the combustion process to generate the necessary power.

However, there are some instances where the combustion process is not as smooth as it should be. For example, some of the air-fuel mixtures get ignited at different times, causing different shock waves that you will experience in knocking or pinging noises. This happens when part of the air-fuel mixture reaches the optimum temperature before your engine is ready to send the spark, and that's why a small portion of the air-fuel mixture will get burned before the rest of the amount.

Some drivers might find it a little challenging to detect the knocking noise because it's not as clear as it should. First, however, think about the knocking noise, like the noise you'll hear when you shake a pair of metal bowls inside a tin bottle. It is more like a pinging noise, as described by automotive experts.

What causes engine knocking?

Knocking is not a good thing, and it can lead to major troubles if it's not only related to issues with their air-fuel mixture because it might be related to tons of other reasons.

Let's take a closer look at what causes engine knocking to understand better the complexity of engine knocking and the possible negative outcomes of this knocking noise:

1-    Low-quality fuel

What is happening?

Not all fuel is the same, and some fuels might come with a different rating known as the octane rating. That's why when you go to a gas station, you'll see different pumps to select from.

Depending on the octane rating, your fuel might withstand higher pressure more than other fuels. The higher the octane rating, the more the fuel can withstand high pressure. Most modern vehicles require a higher octane level to allow the fuel to withstand higher pressure before reaching the ignition point.

How is it important?

As you might already know, the higher the octane level, the more expensive the fuel is. Therefore, many inexperienced drivers think that selecting the lower octane level will save them money. However, that's not the correct choice because depending on your engine; your engine might require a higher-octane level because it's designed this way here; therefore, down the road, you'll deal with major complications, including the engine knocking just because you decided to save on fuel a couple of dollars.

How to deal with it?

You must refer to your vehicle's owner’s manual to get an idea of the minimum octane level required. Of course, you don't want to go below this octane level, but you can freely go with a much higher one. However, it might not be worth the investment going with the maximum octane level because your engine doesn't require it, so you can't consult your mechanic to get an idea about the optimum and most appropriate octane level to select.

2-    Bad ignition timing

What is happening?

Your engine is designed in a way that everything is timed. In other words, whenever the air-fuel mixture reaches a certain pressure and temperature thresholds, the spark plug must send the spark to ignite the air-fuel mixture and generate the energy.

However, spark plugs are expected to fail at some point, which means that they must be replaced. Typically, most spark plugs fail at around 30,000 miles. However, this mileage threshold might differ significantly depending on the type of sparkplug you decide to go with.

How is it important?

If you ignore replacing the spark plug on time, you will deal with problems in the ignition timing. That's when the air-fuel mixture won't ignite at the right time, which might be explained in a knocking noise, and some other symptoms that lead to engine damage are cured

How to deal with it?

To prevent dealing with engine knocking due to bad ignition timing, it is important that you check and inspect your spark plugs regularly and replace them once you hit the maximum threshold. In addition, you want to keep an eye on symptoms indicating a bad spark plug because some spark plugs might fail before their expiration dates which means that you must replace them before then.

3-    Wrong air-fuel mixture

What is happening?

In any combustion engine, the engine requires a specific exact air to fuel ratio. When this ratio is disturbed, you'll deal with engine problems. Most likely, when your engine has a lean air-fuel mixture that you have much more air than fuel, you'll deal with engine knocking.

How is it important?

When the engine receives the wrong air-fuel mixture, you'll deal with a lot of troubles, and this mixture is not expected to reach the optimum temperature and pressure threshold as the one with the right amount of fuel. Therefore, the combustion will not be completed, and the spark might not ignite the rich air-fuel mixture.

How to deal with it?

When dealing with a lean air-fuel mixture, you must review all potential components that might impact it. In other words, if the problem is happening from too much air supply, you want to check your intake valve or probably the oxygen sensor to determine why your engine is receiving more air than it should. Also, if the problem is happening from limited fuel supply, you must determine what's causing this issue and whether there is any clogging in the fuel pathways preventing it from reaching the engine. Finally, whatever is causing the lean air-fuel mixture must be resolved to prevent dealing with knocking noises.

4-    Faulty knock sensor

What is happening?

Automotive experts and manufacturers realized the importance of engine knock troubles. So they decided to install specific sensors to detect engine knock when it's minor and before it gets more complicated. However, these sensors might not function properly, leading to severe engine knocking before any previous warning.

How is it important?

If you rely on the knock sensor to tell you whether the incident as dealing with engine knocking when the sensor is not working properly, you might not know about the problem until it gets to a stage where you must replace the engine because of major damages severe breakdowns.

How to deal with it?

You must inspect the knock sensor regularly as specified in your vehicle's owner's manual to know when to replace it if needed.

5-    Damaged bearing

What is happening?

Your vehicle cylinders are connected to the crankshaft, and as the piston moves up and down, the movement is transferred to the wheels through the crankshaft. The crankshaft is connected to the wheels through some bearings, and these bearings are responsible for ensuring smooth movement back and forth and side to side by the wheels.

Over time of use, these bearings and the rod ends might wear out, causing some issues related to engine knocking.

How is it important?

Ignoring bearing problems leads to severe engine knocking, especially if the bearing problem leads to breaking the crankshaft rod, which is a critical problem and beyond the complications of the knocking noise.

How to deal with it?

It is critical for you as a driver to evaluate when to replace the bearings and keep an eye out for some symptoms indicating a bad bearing before it gets more complicated. Whenever you notice any of these symptoms, it is crucial that you consult your mechanic and replace them or probably replace the entire rod if the problems get more complicated.

6-    Malfunctioning belt and tensioner

What is happening?

Finally, engine knocking might happen due to a damaged belt or tensioner inside the engine itself. These belts are not designed to last forever, and as they're designed from rubber, they can get damaged at some point due to excessive exposure to high temperatures and pressure.

How is it important?

When the belts are not working properly or break, they might lead to loud engine noises that could be in the form of knocking or probably other noises, including rattling or clicking sounds.

How to deal with it?

To get rid of the problem and prevent it from happening in the first place, you should regularly inspect the tensioners and different belts around your engine. Whenever you notice any sign of belt damage, you must replace it immediately. In addition, experts recommend replacing the timing belt even if it's not damaged just in case to prevent dealing with significant complications that easily lead to a complete engine failure.


Any weird noises coming from the engine should not be taken easily. You must take immediate action to prevent dealing with major complications that could cost you the entire engine. Engine knocking is one of those noises you should never ignore because it might be linked to major internal damage.

There are plenty of causes that could lead to engine knocking. Once you understand what causes engine knocking, you'll have a good idea about how to prevent engine knocking and to prevent dealing with situations where you must pay a lot of money on repairs. Typically, engine knocking happens due to issues with the type of fuel, problems with the ignition timing, air-fuel mixture ratios, knock sensor, bearings, and malfunction in tensioners or pulleys.

When engine knocking is linked to a major problem and requires very high repair costs, it is not too late to sell the vehicle and use its money towards a better car that doesn't have any major issues. However, it's not worth your investment installing a new engine, and even if you go with a used engine, there is a very high chance that this problem might reoccur because the used engines are not as good as the brand-new ones.

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