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Knocking combustion – what is it, what are the symptoms and effects?
In order for the engine unit in your car to work flawlessly, you need to take care of the technical condition of almost all of its components. Sensors that regulate the operation of individual engine systems are also very important. One of them is the knock sensor. When this part is damaged, the engine stops working properly due to the improper parameters of the fuel-air mixture in the cylinders. Go further and find out what knocking combustion actually is and how to avoid engine problems. This is important if you want to travel safely and without failures!
From this article you will learn:
- What is combustion knock in engines?
- What are the symptoms and causes of combustion knock?
- What type of damage can occur during combustion knock?
- Is combustion knock dangerous?
- How to prevent engine knock?
Also read the guide: Engine oil markings – how to read them and what are the types you need to know about?
Can knocking combustion damage the engine unit? You need to know!
According to the principle of operation of a combustion engine or diesel engine, a mixture of air and fuel is burned in the cylinders of the unit. For the engine to work properly, the right proportions of these factors are necessary. This means that damaged knock sensor can lead to engine destruction, e.g. due to a sudden increase in temperature in the combustion chamber.
Do you know that…? The knocking combustion process is a chain reaction with an element of detonation. When a problem occurs, you will initially hear a distinct knocking sound from under the hood. If you do not react quickly enough, the piston, connecting rod, piston rings and entire cylinders can be damaged.
The main causes of the knocking problem are:
- engine overheating, e.g. when driving short distances at high revs;
- incorrectly set ignition advance;
- knock sensor damage;
- poor quality fuel;
- too high compression of the fuel-air mixture in the cylinders.
In practice, knocking combustion can have a negative impact on the engine condition, for example due to: accelerated wear of the crank-piston system. Imagine that these moving parts will be deformed by too high temperatures in the combustion chamber… it is a sure way to seize the engine and then the repair costs can be really high!
Curiosity! A single combustion cycle of the fuel-air mixture in modern passenger cars lasts about 0,001 seconds!
Read also: Which engine oil?
What are the symptoms of combustion knock and how to recognize the first problems?
When it comes to consequential combustion, the causes can be various, such as improperly operated vehicle or simply a damaged combustion sensor. You have no idea how to recognize such a problem by its symptoms? It's not that difficult. When you start your car or while driving, you may notice or hear…
- uneven engine operation, especially at idle speed – then fluctuations on the tachometer will be visible to the naked eye;
- metallic knocking noises from under the hood, resembling a damaged bearing shell;
- the "check engine" light on the dashboard – of course, without a computer you won't learn anything more about it;
- noticeable increase in fuel consumption while driving and a drop in power.
If you don't diagnose the damage to the combustion sensor quickly enough, the symptoms can be much more serious. During regular service work, you will definitely notice increased engine oil consumption (manufacturers protect themselves by indicating that the approximate engine oil consumption is often about 1 liter per 1000 kilometers).
What to do when engine knocking starts?
Above all, stay calm and try to get your car to a mechanic as soon as possible. Metallic sounds, excessive fuel consumption and lack of power are just the beginning of bigger problems… Knock-off combustion can burn holes in the pistons and also break the timing belt, and then you will have no choice but to replace the engine with a new one… or the whole car.
Due to the fact that this is one of the most dangerous failures for combustion engines, immediately after its detection you should:
- Stop the vehicle if you feel that continuing to drive could result in more serious damage.
- Make an appointment with a service center for a precise diagnosis of the fault and repair.
Never try to continue driving at all costs. This is a sure way to completely destroy the engine.
Damaged knock sensor – how does this sensor work and where to find it?
When the engine is not working properly and you suspect that the knock sensor has been damaged, you can start diagnostics from this part. The sensor is most often found on the engine block, intake manifold or directly on the cylinder.
The sensor detects vibrations of the engine block and converts them into electrical signals. The controller then analyzes the transmitted data and manages the engine's operation, e.g. in the process of burning the fuel-air mixture in the cylinders.
Remember! The knock sensor is directly responsible for the ignition advance angle on individual cylinders.
So if the sensor is damaged, then in 99% of cases the engine will stop working properly. In most cases, it is enough to replace the sensor with a new one to get rid of the problem and avoid the risk of more serious faults.
Why is combustion knock dangerous for your car's engine?
This phenomenon can be really problematic, especially if you do not react in any way and continue to use the vehicle at all costs. The increase in combustion temperature and pressure can lead to damage to the cylinder head (repair requires so-called cylinder head planning, i.e. leveling of its surface), as well as burnt valves.
In extreme cases, the engine may also seize completely, for example, the pistons may be damaged or the crankshaft may even break. Such situations may make the car completely unprofitable to repair.
See also the article: Differences in premium and standard fuels – is it worth paying extra?
How can you effectively prevent combustion knock?
The causes of combustion knock often stem from the negligence of the vehicle owner. If you do not maintain your vehicle regularly engine oil change or you forget about regular visits to the service… probably problems with combustion knock will appear at the least expected moment.
What can you do to avoid problems with improper combustion of the fuel-air mixture in the engine? Use a few practical tips:
- try to use high-quality fuel, preferably the one recommended by the vehicle manufacturer;
- Change the engine oil regularly – although many manufacturers’ recommendations vary, it is worth doing it every 10 kilometres or once a year;
- check the condition of the spark plugs – you must assume that the real problem-free mileage without replacement is 20-30 thousand kilometers.
Also try to regularly check the condition of the sensors in the engine, e.g. the knock sensor. Such actions, combined with cyclical engine flushes (in this case, remember to use only recommended engine preparations) and checking the correct vehicle controller settings by a service technician is the basis for avoiding serious problems with knocking combustion in your car.
FAQ
Can I continue driving my car if knocking occurs?
No. If you hear metallic knocking or the engine starts to run strangely, stop as soon as possible. Continuing to drive can destroy the engine, so take your car to a mechanic as soon as possible.
Does combustion knock always mean that the engine is already damaged?
Not always. If you react quickly, it is often enough to replace the sensor or adjust the ignition. But if you ignore it, it can cause expensive damage – to the pistons, valves, head.
Does fuel quality affect combustion knock?
Yes. Cheap, low-quality fuel is one of the main causes of combustion knock. Refuel at trusted stations and use fuel recommended by the car manufacturer.
Does engine tuning increase the risk of engine knock?
Definitely yes. Changing the ignition map, increasing power, or installing a turbocharger without proper tuning can cause combustion to be too aggressive. Without a good ECU setting, the risk of knocking increases.
