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6 Causes of Engine Knocking (and How to Fix Them)

Car engines can make many different noises and some are louder than others.

Engine knocking is one of those noises that you don’t want to hear from your car’s engine because it can damage many internal parts of your engine.

Fortunately, engine detonation is usually fairly easy to eliminate. In this article, we will talk about the most common causes of engine knocking and how you can fix the problem. Let’s start with a quick overview of common causes:

The most common cause of engine knocking is the wrong type of fuel in your car or a faulty knock sensor. Incorrect ignition timing, a lean fuel mixture, or the wrong type of spark plugs can also cause your engine to stall.

These are the most common reasons why engine knocking occurs. Here is a slightly more detailed list of the most common causes of a knocking car engine:

Causes of car engine knocking

1. Low octane

fill the car

The most common reason why your engine knocks during acceleration is that you have the wrong fuel in your car or simply low-octane fuel.

Either you filled up the wrong type of gas the last time you went to the gas station, or the gas station simply had the wrong fuel in its tank.

If you get low-octane fuel in your fuel tank, premature combustion can occur. This will cause the engine to knock.

If the problem occurs after refueling and you have filled the tank with gas, you can try using an octane booster to increase the octane a little instead of replacing all of the fuel in the tank.

2. Defective motion sensor

Engine knock sensor

The next common cause of engine knock is a faulty knock sensor. The knock sensor is designed for exactly this purpose: to prevent the engine from knocking.

The engine control always wants to have the ignition as advanced as possible to obtain maximum performance. If you fill your tank with low-octane fuel, the engine will require slower ignition timing to run without knocking.

Therefore, the job of engine knock sensors is to monitor for any knocking and, if so, tell the engine to delay ignition further to prevent engine damage. If this engine knock sensor has gone bad, it can send false signals to the engine control unit, which will cause the engine to knock.

3. Poor ignition timing

Ignition time

Ignition timing too late will cause the engine to start knocking or rattling. For this reason, faulty ignition timing could of course cause engine to knock.

Unfortunately, this only applies if you have an older car with adjustable ignition timing on the distributor or an adjustable cam or crankshaft position sensor.

Newer cars control ignition timing completely electronically, so you won’t be able to adjust the timing.

However, if you have an older car with adjustable ignition timing, you need an ignition timing lamp to check the timing. Try delaying the timing a little to see if that helps with engine knock. However, it is recommended to follow the repair manual for the correct ignition timing.

4. Lean air/fuel mixture

engine knocking

You may not know it, but the fuel entering the engine also cools the combustion chamber. If the air-fuel mixture is too lean, it will not cool as efficiently and will generate a lot of unnecessary heat in the combustion chamber.

This heat can cause the air-fuel mixture to ignite itself before the spark plug fires its spark, causing the engine to start. These types of destinations are dangerous to the internal parts of your engine and can melt your pistons quickly.

5. Defective spark plugs

The best spark plugs

It’s not very common for bad spark plugs to cause your engine to knock or explode, but it absolutely can happen.

Spark plugs provide the ignition spark to ignite the air-fuel mixture. However, there are many types of spark plugs, and if you purchase the wrong type of spark plug, your engine may begin to suffer from knocking.

In the first case, the spark is too weak, while in the second case, the spark plug may not produce any spark at all. Consult your repair manual to find the correct spark plugs for your car model and make sure the correct model is installed.

6. Other engine knocking noise

Serpentine Belt Components

There’s also a chance that it’s not a clunking or pinging sound you hear from your engine; It could be another type of engine noise.

If you hear knocking only when accelerating, it’s most likely the engine knocking or pinging, but if you hear the noise constantly, it could be caused by something else.

Some other common things that can cause knocking noises are timing belts or coil tensioners/pulleys, bad connecting rod bearings, bad hydraulic lifters, or noisy fuel injectors.

Learn more here: 5 Common Car Engine Noises

What is engine knock?

Engine knocking or knocking occurs when the air-fuel mixture automatically ignites before the spark plug ignites it, due to high heat. This can be caused by poor ignition timing, too low a fuel octane rating, or a lean air-fuel mixture.

When the engine is revving, the air/fuel mixture will ignite halfway and as you can imagine, this will cause incredible pressure when the piston is halfway up. It can also generate incredible heat that can melt holes in your pistons or cylinder heads.

That is why it is a good idea to fix your engine knock in time and it is better not to drive it.

How to fix engine knock

Mechanics Diagnose Car

Now that you know the different things that could cause engine knocking, you probably also want to know how you can fix it.

The first thing you should think about is when the bumps appear. If this happens after refueling the car, you probably have bad fuel in the fuel tank. To solve this problem, you should replace the fuel or try using an octane booster.

You can also check for trouble codes related to knock sensors with a diagnostic scanner. If you find any trouble codes related to this, it is definitely time to fix the wires or replace the knock sensor.

You also want to check the spark plugs to make sure you are using the correct type of spark plug for your car’s specific engine. Use your repair manual to find the correct spark plugs.

If you have an older car or the car engine has an adjustable ignition timing, you should definitely check and adjust it. Check your repair manual to find out if it has adjustable timing or not.

Let a repair shop do it if you are not familiar with timing adjustments, as you also need special tools for the procedure.

Engine Knock FAQ

What does the engine sound mean??

The engine noise makes it sound like someone is sitting and hitting the engine block with a metal hammer when you accelerate. If you hear a knocking noise only when accelerating, the engine is most likely knocking or pinging.

How to stop the engine from knocking?

The first step to stopping engine knock is to make sure you have fuel with the correct octane rating for your car model. You can try using an octane booster to make it less susceptible to explosions.

Can you drive a car with a knocking engine?

It is not recommended to drive a car with a knocking engine. Engine knocking or so-called detonation is very dangerous to the internal parts of your engine, which can result in repair costs of over $3,000 if you are not careful.

How much does engine knock repair cost?

There is no set price to repair a knocking engine. Often it is enough to use octane boosters or fill the fuel tank with fresh fuel. In the worst case, you need to adjust the ignition timing or replace the knock sensor. However, you can expect a cost of $100 to $200.

Can lack of oil cause engine knocking?

Engine oil is not related to ignition timing or engine knock in your car. This could affect you indirectly, although if you have such a low engine oil level, it causes low engine oil pressure.


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