Knock, knock. Who is there? A pesky and consistent noise when you drive. If the soft rumble that your car makes when cruising down the street is replaced by a constant knocking or tapping sound that gets louder when you brake or accelerate, then it is a telltale sign of a common problem called the engine knock.
It is crucial to keep in mind that ‘engine knock’ can relate to and signify a varying range of noises and each noise could relate to something different; hence figuring out the origin of the noise could be rather challenging.
A few of the main reasons behind a knocking noise from your engine are issues with oxygen sensors, detonation issues, worn-out rod bearings, and faulty belt pulleys.
We have listed below the reasons with their possible solutions to assist you to figure out this tricky part with ease!
Table of Contents
6 main reasons why you are hearing a knocking sound when applying brakes
Reason #1 – Bad belt pulleys
One of the main reasons for engine knocking could be originating from somewhere besides the engine as well. It could be originating from the accessory belt. As the engine functions and runs, it turns around a belt that is connected to the multiple pulleys throughout the engine bay.
This particular belt must be experiencing the exact and right amount of tension so that it runs and turns smoothly. In case the belt becomes too stretched out, one of the pulleys bends with gradual use, or if the tensioner is not working correctly, you will probably hear rattling, slapping, and clicking noises that can be easily mistaken for engine knock.
Solution: To fix a rather noisy accessory that rattles around under the hood, you would need to acquire the help of your local mechanic. With his expertise and tools, you should be able to get the accessory belt repaired or replaced, get the tension adjusted, or even replace a poor tensioner or accessory pulley.
Reason #2 – Rod Knock (Worn out bearings)
Another sort of engine knock is the rod knock. As the piston retracts in and pushes out in the engine, it turns the crankshaft which ultimately powers the engine and helps the car run. The rod bearing facilitates smooth movement of the piston, but like any other component, it can become worn down or move out of position with gradual and continuous use. As and when the bearings wear out, the piston will begin to rattle against the crankshaft, producing a sound similar to engine knocking.
Solution: To fix this particular issue with rod bearings, you would need to acquire the help of your local mechanic who can either replace the rod bearings or figure out what is exactly wrong with the piston’s crankshafts. These repairs are usually time intensive.
Reason #3 – Detonation knock (Bad knock sensor)
Thankfully, engine knock is not a problem that one will encounter often in modern cars since the air-fuel ratio and the timing of the fuel injectors are all controlled by computing processes. There is also a knock sensor that is customized to detect engine knock and signal to the ECU, after which the ECU tries to eradicate the problem.
Solution: This automatically means that the bad knock sensor will allow the engine to knock while trying to fix the issue internally. If you own a relatively modern car, it is essential to pay attention to the knock sensor which can help you pinpoint the problem and you can consult your mechanic accordingly.
Reason #4 – Detonation knock (Poor air-fuel ratio)
Issues originating within the fuel pump, oxygen sensors, fuel injectors, and mass airflow sensors are likely to produce a lean air-fuel combination. A lean air-fuel mixture refers to a mixture that does not have an adequate amount of fuel and much more air.
Without proper fuel in each cylinder, the combination will not combust fast enough, leading to multiple detonations that we call the engine knock.
Solution: To figure out and pinpoint the exact issue within the oxygen cylinders, fuel pump, mass airflow sensor, and fuel injectors you would need to acquire the help of your local mechanic. He can inspect and judge the situation and figure out if any of the cylinders need to be repaired or replaced.
Reason #5 – Detonation knock (Poor timing)
In most modern and newer cars, the timing of the engine i.e., at which moment in the engine’s journey the spark plugs will fire, is controlled by a computer. But in case, for any possible reason, the sparks are not firing at the moment they should; this can lead to multiple detonations within the cylinder, leading to what we hear as engine knock.
Solution: Since this is a relatively complex issue and would require particular tools and skills to resolve, it is best advised to acquire the help of a local mechanic. He can properly check which spark plug is firing and which one is not and repair or replace them accordingly.
Reason #6 – Detonation knock (Low amount of Octane)
If you are not already familiar with the definition of a detonation knock, let’s break it down. In a usual case whenever your engine is functioning perfectly fine, typically the air-fuel mixture combusts within one highly calculated detonation within every cylinder.
You are likely to hear this type of sound if the air-fuel combination within each cylinder begins detonating multiple times in a single shot.
A bit of the air-fuel mixture might ignite sooner than needed and as these tiny balls of fire come in contact with each other, they create what we hear as a knocking sound.
Note: In case your car is equipped with a specifically tuned performance engine that is rated suitable for fuels with higher octane, then you can expect to hear a knock in case you use a fuel with a lower octane rating than usual. Higher octane level fuel burns much more consistently and resists knock.
If you use unleaded fuel into your vehicle that needs superior quality fuel; you are bound to hear a knocking sound.
Ensure to check the owner’s manual to determine the suitable octane amount that works best for your vehicle.
Solution: After ensuring that you have not simply used the wrong type of fuel for your vehicle, and if you are sure that the issue lies within the quality of the air-fuel mixture and cylinder function, it is best advised to acquire the help of your local mechanic. He can pinpoint the issue with the help of particular tools and replace or repair whatever is required.
Conclusion
The knocking sound or engine knock can be caused by various reasons and some of them are not even related to the engine. Engine knocking is an annoying indication that something is wrong with the fundamental functioning of the car, and usually, it is caused by malfunctioning fuel injectors, oxygen sensors, belts, and more.
You need to take your car in to get checked out by a professional at the earliest to prevent any further damage from occurring to components. It is best not to stress the car further if it is already exhibiting issues.
