engine knocking

Engine knocking – What does it mean & How to fix it?

In Engine by Magnus SellénLeave a Comment

car engine repairA good car engine should run smoothly with little noise.

However, if your car produces rattling, ticking or knocking sounds it could be a sign of engine trouble.

Engine knocking is produced when the car’s fuel burns unevenly. Instead of proper combustion, you have a lot of unburnt fuel. If you hear a ticking sound the problem could be a lack of lubrication on in the combustion chamber. 

You can also have a detonation – Which means that the fuel is burned too early which is causing the combustion is pushing the piston down before it has even reached up to the top. This can be very dangerous for your engine and should be fixed as soon as possible.

Reasons why your Car engine is knocking

In this regards, you will need to check your engine for oil leaks. Below is a list of possible causes for engine knocking.

1. High carbon deposits

Unburnt fuel will lead to high carbon deposits. Fuel has a high carbon component and this often remains after combustion. With time this carbon deposits increase causing the inefficient combustion. You can solve this by adding a carbon cleaning detergent in your fuel.

2. Wrong spark plugs

Spark plugs provide the spark for the ignition of the fuel/air mixture. However, if you purchase the wrong type of spark plugs you will experience engine knocking. In most cases, the wrong spark plugs will have a gap that is too narrow or too wide.

In the first instance, the spark is too weak while in the latter the spark plug may fail to produce a spark. Ask your mechanic to recommend the right spark plugs for your car.

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3. Using fuel with a low octane rating

engine knockingThe fuel/air ignition should happen at the right time. If you purchase fuel with a low octane rating then you may experience premature combustion. This will cause engine knocking. To solve the problem always purchase fuel that has a higher octane rating than what is recommended by the manufacturer.

If you still have the low octane rating fuel, you can add an octane booster to rectify the problem.

4. Improperly lubricated cylinders

The combustion cylinder needs to be properly lubricated for it to function well. When this is not done you will have the cylinder knocking against the walls. The main problem is that the cylinder is not receiving the right amount of lubrication due to loose valves or lifters. An oil leak could also lead to the cylinder head receiving less oil.

5. Unbalanced air/fuel mixture

For the engine to perform smoothly there is a need for the right amount of the air to fuel mixture. Too much fuel and you have uneven combustion. This further leads to damaged pistons and cylinder walls. You will then be forced to replace this immediately, otherwise, you will further destroy your engine. check your fuel injector sensors for any dirt accumulation.

6. Wrong Ignition timing

If you have an older car, with a distributor which can be adjusted, there is a chance that the ignition timing is too advanced, which can cause detonation.

How to fix engine knocking

Getting the right fuel

When fuel has a high octane rating it tends to burn slowly while those with low octane ratings burn faster. High-performance cars like sports cars use gas with high octane ratings while normal cars tend to use those with lower ratings.

If you have a car with a carburetor then the fuel efficiency is reduced and you may be forced to try out some high octane gases. Modern cars have the latest fuel injection technologies and this eliminates the need for fuel adjustments. For most cars the best octane fuel rating is 87.

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Buying the right spark plugs

Cheap items are not necessarily cheap in the long term. You can purchase some plugs hoping to save on some dollars only to realize that they cause more harm to your engine. Ask your mechanic to get you the manufacturer’s recommended spark plugs.

They often go for around 10 dollars but you will need to pay the mechanic extra for installation.

Manage boost pressure

If you have too much boost in your car it can lead to premature detonation. In this case, you will need to modify your engine to accommodate the boost. If you are using a turbo then it is prudent to modify your wastegate so that it dissipates the excess pressure. In this instance, you will have the turbo producing more boost when their leaks in the vacuum connections.

Adjust air/fuel mixture

When your fuel injectors are not working properly you will experience detonation. Lean air/fuel mixture can be as a result of leaking vacuum lines or the gaskets becoming worn out. In this instance, when the car is at idle you will find some hesitation when you accelerate. Have your mechanic check for clogged carb jets, dirty fuel injectors or a restricted fuel filter.

Remove carbon deposits

Fuel is made from carbon molecules. These often accumulate in the combustion chambers hence reducing the engine efficiency. A dirty engine will have carbon deposits on top of the pistons and this can affect the compression of air/fuel mixture. Too much carbon deposits will cause detonation. A chemical cleaner can be used to remove the deposits.

Fix the knock sensors

A knock sensor is a modern innovation in many cars. It works by detecting vibrations within the combustion chambers and sending this information to the ECU. If detonation is detected the onboard computer will momentarily stop ignition. However, the sensors do become faulty with time and this means you the ECU will not be able to control detonation.

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Keep your compression ratio reasonable

For most cars, the recommended ratio is 9.0:1. This is not the case for cars that have knock sensors where you can have higher compression ratios. If you need a boost then you can go for lower static ratios of below 8.0:1.

Unless you plan on using racing fuel it is recommended that you keep your compression ratios within the recommended range. You can try to use cylinder heads that contain larger combustion chambers or head gasket shim that is made from copper.


The main cause for engine knocking is when you have a large amount of unburnt fuel. This finds its way to the engine exhaust and you will notice a smell of rotten eggs. Engine knocks can lead to further engine damage if not rectified immediately. To reduce engine knocking ensure that you use fuel of low octane rating. You should check the manufacturers manual for the right fuel for your engine.

Hello I'm Magnus, the owner and the writer of this website. I have been working with cars since I was 16 and I'm specialized with in-depth Automotive diagnostics. Also been driving drifting for the last 6 years. I'm here to give you answers to all your automotive questions and I hope that you enjoy our content.

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