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What Causes Engine Knock?: Everything You Need To Know!

What Causes Engine Knock?: Everything You Need To Know!

To determine what causes engine knock in your vehicle, you need to figure out first what engine knock is, how to detect the knocking, how to predict that engine knock may occur, and how to control the knock for the future. Unfortunately, engine knock can mean one of several different problems. Luckily for you, we are here to help you figure out where the problem is coming from, the signs of a problem, and how to fix it. Let’s dive a little deeper into the real details about engine knock in your vehicle.

Auto Repairs Are EXPENSIVE

First up – what is engine knock?


Knocking, also known by other names like detonation, spark knock, or pinging, in spark-ignition internal combustion engines, this occurs when combustion of some of the air and fuel mixture does not cause a flame or a spark in the spark plug, but instead, a pocket of air and fuel mixture explodes outside of the normal combustion mechanism – a dangerous and deadly combination.


The air and fuel mixture in your car is a mass ratio of air to a solid, liquid, or gas fuel that is present during the combustion process. The combustion might happen in a small manner, like internal combustion, or can result in an explosion – which is bad for you and your car. 


This precious mixture in your car is supposed to ignite by the cause of the spark plug, and only at one specific point during the piston’s stroke, but sometimes – this can backfire. Knock often occurs when the height of the combustion process doesn’t operate at the right time during a four stroke cycle, which is when the piston completes four separate strokes while turning the crankshaft. 


This shock wave then creates the “knocking” sound that, in turn, causes the aptly named engine knock. This sound causes pressure to dramatically increase, causing various issues with your vehicle, either minimal – or extremely destructive.

So – what is abnormal combustion like in my car? How Do I Know It's an Engine Knock?


If the fuel and air mixture is exposed to the right combination of heat and pressure, this can lead to an explosion or detonation. Detonation is when an explosive ignition of one pocket of air and fuel, or more, occurs outside of the flame front, creating a shockwave, and enhancing cylinder pressure. 


If this harmful detonation continues to occur over various conditions and occurs many times, engine parts can be severely damaged and destroyed, leading to necessary repairs and replacements. Such effects can be erosion, holes melted through the piston or cylinder head, or leaking combustion products into the oil system. 


Detonation can be prevented by following some useful methods that all car owners should know about engine knock. Try utilizing one of these techniques, by reducing peak cylinder pressure, decreasing the manifold pressure, reducing engine load, using a fuel with high octane rating, and enriching the air to fuel ratio which can reduce the combustion pressure and temperature. 

The Main Causes of Engine Knock


Engine knock can be caused by many things in your vehicle. However there are a few main causes which you should consider before trying to diagnose your vehicle.

Low Octane Rating


First, the fuel in your car can have a low octane rating. The octane rating is the standard measure of performance of an engine or gasoline, with the higher octane rating being the better number for your vehicle. Manufacturers generally recommend a certain amount of octane as a minimum to obtain a high performance in your car – if you don’t use this number, then your vehicle will not run smoothly. 


If you use gas that has too low of an octane rating then you can help boost your gasoline by adding an octane booster. If you do not use the right fuel for your car, the combustion of the premature detonation of the air and fuel mixture can cause the engine knocking sounds in your heart. 

Carbon Deposits


Second, the next main cause of engine knock is that carbon can deposit on the cylinder walls. All fuels that you may use in the United States are generally required to have a certain level of cleaning detergent in them, ensuring carbon does not stick. Although this is the law, some stores do not keep up with this requirement, meaning deposits can form on your cylinders, and the volume of the cylinder is decreased – causing engine knock. 


To fix this, try adding detergent additives to an auto parts store and try switching the fuels you normally issue. In most cases, using a certain fuel injector cleaner or an additive that is specially designed to clean the carbon deposits on the cylinder walls on the engine components can help resolve this issue over time, and is a relatively inexpensive way to help save your vehicle. 

Engine Timing


Third, the timing of the engine is crucial for the spark plug life and the engine knock prevention. The timing of the engine controls at which rate the spark plugs fire in your car. If this is incorrectly controlled by the car’s computer, then this can cause detonations within the cylinder and lead to engine knock, since the spark isn’t firing when it should. 


The spark plug gap is the palce where the spark plug itnites the air and fuel mixture that helps to run the car and power the negine. If this gap ebtween spark plugs ends up being too anrrow, this can create a spark that is not powerful enoguh to perform the task, and too wide of a gap might rpevent a spark from being able to fire at all, leaing to a rrapid misfire. 

Sensor Issues


Fourth, your car may have problems with oxygen sensors, fuel injectors, fuel pumps, or the airflow sensor, causing an engine knock due to the lean air and fuel mixture within the engine. A “lean” fuel and air mixture means that the mixture of gas and liquid has too much air and not enough fuel, meaning that without enough fuel, the mixture won’t be able to burn at the correct rate and allow for multiple detonations – causing engine knock.

Bad Knock Sensor


Fifth, your car could have a bad knock sensor, since this problem is generally uncommon in most modern cars due to the other reason.s In modern cars with higher technologies, the air and fuel ratio, the fuel injectors, and the timing of the sparks are all computer controlled, leaving little room for error. There is even a knock sensor used on modern cars that is supposed to detect engine knock and alert the Engine Control Unit so it can fix the issue in your vehicle almost right away. However, if you have engine knock in a newer car, this can mean that your engine knock sensor is bad. 

Rod Rock


Sixth, your car could also be suffering from rod knock. This is a type of engine knock that occurs when the pistons travel up and down the engine, sending power to the wheels, allowing the rod bearings to allow for smooth piston movement – but unfortunately, these rod bearings and pistons get worn out over time. As the bearings wear down the crankshaft, the sound can resemble engine knocking, meaning that you might need a new crankshaft – which can be a very costly repair. 

Non-Working Belt Tensioners 


Seventh, you might have bad belt tensioners and pulleys, causing engine knock in your car. Although this is cooled engine knock, the issue might not be coming from the engine itself at all, but instead, the accessory belt. This belt is a pivotal part of the engine, turning as the engine runs, connecting to various pulleys. In order to operate smoothly, this belt must be under the right amount of tension, meaning that if it becomes too stretched out over time, it can get bent out of shape and harm the pulleys, causing a clicking and rattling noise that could be oftentimes thought of as engine knock.

Wrong Spark Plugs


Lastly, the main cause of engine knock is that your vehicle has the wrong spark plugs for the make and model. Manufacturers have a certain level of spark plugs that are recommended for each individual vehicle, so if the spark plug is incorrect, the plug may not do its job to withdraw heat from the combustion chamber. 

How Do I Detect Engine Knock?


Many engines in modern cars now contain various technologies and mechanisms that can detect a knocking from the engine or change the pressure according to what you need done, and can improve performance and reduce the risk of engine knock while running on low octane fuel.


An example of one of these systems is the Automatic Performance Control in Saab engines, which was the first engine knock and boost control system that was introduced to all Saab H engines in 1982.


Other monitoring devices are used, like tuners to listen and see if the vehicle is under a safe load, preventing engine knock. 

How Can I Predict Engine Knock?


Since you really want to avoid the occurrence of engine knock to enhance the lifespan of your car and keep it running safely, various technologies have been developed that can identify certain engine types or designs that are more privy to engine knock than other options.


Since the onset of engine knock is sensitive to the in-cylinder pressure, temperature, and chemistry related to the composition of air and fuel within the combustion chambers, there are certain simulations that can determine the best operating methods for these specific technologies. 

How Can I Control Engine Knock?


When preventing engine knock in your vehicle, the main method is to attempt to protect the engine from the knock, and maximize the output torque – thereby not affecting the performance without putting yourself and your car at risk. Unfortunately, science engine knocks are random and independent of other situations, they can be difficult to control and determine the best methods to provide a repeatable outcome of prevention. 

How Can I Fix Engine KNock?


Despite engine knock not being the easiest problem to fix on your car, there are a few common solutions that can ease or fix the knocking issues. 


First, you might need to replace the timing belt. Most cars today are four-cylinder vehicles, using a rubber belt to control the timing of your engine and firing. As we know, the belt needs to be at the right tension to function properly. Try replacing the timing belt at the recommended intervals for your specific vehicle to ensure it doesn’t get stretched out and to line everything up properly in your car once again. The replacement of a timing belt is one of the most expensive car repairs when dealing with routine car maintenance. The average price of replacement costs between $500 to $2000.


Second, you might need to change the fuel you are using. The fuel-related engine knock is because the fuel that you are using doesn’t have the right octane rating for your car, so you might need a higher level of octane rating and switch to premium fuel before your car detonates. 


Third, you might have to replace the engine bearings in your vehicle, which will require you to go to an automotive store to get the experience of a trained professional. The mechanic will need to reset the bearings that have become displaced due to the vibrations of your engine knock, so it’s best to leave this solution to the professional. 


Lastly, you might need to replace the engine crank. This is one of the most common mechanical reasons that your timing could be off, causing the engine knock sound. A broken crank doesn’t allow the pistons to fire at the correct time, leading to multiple issues in your car, like bad bearings, secondary explosions, and other even more deadly issues. This is an intensive repair like the bearings, so you will need to go to a professional shop to get this done. 


There you have it! Now you know what an engine knock is, how to detect an engine knock in your vehicle, the signs of engine knock and the process of abnormal combustion, the main causes of engine knock, and the steps to fix the engine knock. 


By knowing how to determine if your car is suffering from engine knock and knowing the right steps to fix it, you can save yourself thousands of dollars in repairs, or save your life and those of the others in your car.