Engine Knocking: What is it and what could be the cause of it

Everyone may agree that cars can create strange noises. It could be a screech, a clang, or even a rumbling and roar. If the sound is more akin to a “knock,” you may be dealing with issues under the hood—issues that, if left unaddressed, could cause engine damage.Engine knockingWell, in this article, the answers to the following questions will be discussed:

  • What is engine knock?
  • Why is an engine knocking?
  • Is it safe to drive if I hear an engine knocking?
  • What should you do if your car engine is knocking?

So, let’s get down to it!


What is engine knock?

Engine knocking


Engine knock is a tapping, pinging sound that increases in volume and annoyance as you accelerate. When fuel burns unevenly in your engine’s cylinders, it causes knocking. When cylinders have the proper air-fuel balance, fuel burns in discrete, regulated pockets rather than all at once. (Think sparklers rather than fireworks.)

After each pocket burns, it produces a little shock, which ignites the next pocket and continues the cycle. Engine banging occurs when the fuel burns unevenly and the shocks activate at the wrong time. The end result? An obnoxious noise and the possibility of cylinder wall and piston damage in your engine.

Why is an engine knocking?

There are several causes for an engine knocking, including:

  • A faulty or improper spark plug
  • Low-quality or low-octane fuel
  • Wrong ignition timing
  • Mixture of Lean Airfuel
  • Crankshaft Damaged or Broken
  • Serpentine Belt Extending
  • Bearings that have worn out
  • A faulty knock sensor
  • Non-Lubricated Cylinder Head

A faulty or improper spark plug

Spark plugs are in charge of producing the spark in your engine’s combustion chamber. This spark ignites the air-fuel mixture, resulting in engine power. Premature detonation within the combustion chamber may occur if your engine has a faulty spark plug or spark plugs that do not meet the criteria of the specific engine. This can result in a detonation knock on the engine.

Low-quality or low-octane fuel

Every fuel type is assigned a number based on its octane rating. The higher the octane rating, the more refined the fuel. In other words, the higher the amount of octane, the more regulated the detonation of air fuel. When you put low-octane gasoline in your car, it might cause the airfuel mixture to burst prematurely, resulting in an engine knocking sound.

Mixture of Lean Airfuel

To continue with the combustion concept, the “spark” supplied by the spark plugs ignites a compressed air-fuel mixture. Multiple detonations and a loud knocking engine noise occur when there is a low proportion of fuel in this mixture. Check and inspects the engine components that control the flow of air and fuel within the engine, such as the fuel injectors and mass airflow sensors, as these have an impact on your air-fuel ratio.

Carbon deposits

In order to prevent carbon deposits from clogging your cylinders, every fuel sold in the United States must contain carbon-cleaning chemicals. Unfortunately, some deposits remain. When this occurs, there is less space for the fuel and air to reside, resulting in higher compression. Changes in fuel compression, as you know with fuel, can cause unpleasant knocking sounds. Excess carbon build-up can disrupt the combustion process and damage the cylinders of your engine. The consequent drop in performance can potentially result in decreased gas mileage or overheating.

Crankshaft Damaged or Broken

Inside the cylinders attached to the crankshaft, the piston rings of your car’s engine travel up and down. The engine timing system controls this. The rods and bearings that connect the cylinders to the crankshaft are critical for maintaining optimum cylinder-to-crankshaft clearance. When the crankshaft is damaged and the clearance between the cylinders is not properly maintained, metal-on-metal contact can occur, resulting in a rod knock.

Wrong ignition timing

When the ignition timing is too advanced, the engine will begin to knock or ping. As a result, wrong ignition timing could result in an engine knock. This only applies if your car has adjustable ignition timing on the distributor or an adjustable cam or crankshaft position sensor. Unfortunately, because contemporary cars manage the ignition timing entirely electronically, manual adjustment is not possible. To check the timing on an older car with changeable ignition timing, you’ll need an ignition timing light. Try slightly delaying the timing to see if it helps with engine detonation. It is, nevertheless, suggested that you use the repair instructions to ensure proper ignition timing.

Serpentine Belt Extending

When a car’s engine runs, it rotates a serpentine belt that connects to multiple pulleys (which power various accessories) around the engine bay. This belt must have precisely the correct amount of tension to spin silently and smoothly. An overly stretched belt will be unable to maintain the proper degree of tension, resulting in rattling, clicking, or screaming noises that can be confused with normal engine noise.

Bearings that have worn out

As your car ages and the engine wears out, the bearings on the connecting rod between the cylinders and the crankshaft can begin to fail, resulting in a rough ride with a loud rod knock. Particles accumulate in the engine as cars age, and combustion by-products such as carbon deposits, dirt, and grime can collect at the back of the rod bearing. These will damage the connecting rod, resulting in a piston slap or knocking sound instead of smooth movement. Because rod bearings are placed deep within the engine, you should have a mechanic repair them.

A faulty knock sensor

Most modern vehicles include a knock sensor, which detects engine banging and delivers data to the Engine Control Unit (ECU). The ECU then automatically corrects the problem. If your knock sensor is damaged or broken, the engine will continue to knock. A faulty knock sensor will also illuminate the check engine light.

Non-Lubricated Cylinder Head

Lubrication is required for all engine cylinders. Unlubricated cylinders make a knocking sound. When there is an engine oil leak, a cylinder will normally lose lubrication. Using generic oils with lower flashpoints might also result in poor engine lubrication. As a result, several automakers advise using synthetic engine oil to lubricate the cylinder head. Unlubricated cylinder heads can also harm the piston rings and cylinder wall, making this a must-fix to avoid piston slap. If you discover an oil leak, place an oil pan below your car to catch any leaking engine oil before changing the oil.

Is it recommended to drive if you hear an engine knocking?

A knocking sound is frequently the result of an issue with an engine’s internal components. It is not recommended to drive if you hear a knocking noise. The greater the engine damage to these core components, the more complex and expensive the repair process. It’s possible that you’ll need to repair expensive engine parts. The check engine light will illuminate for the majority of the issues that produce an engine knock, so keep an eye on it and don’t let engine wear become a long-term problem.

What should you do if your car engine is knocking?

You’re undoubtedly curious about how to remedy the engine knock now that you’re aware of the various causes. The first thing you must consider is when the knocking occurs. If it happened after you refueled the car, you most likely have contaminated fuel in the tank. To correct this, either replenish the fuel or try using an octane booster.

You can also use a diagnostic scanner to look for any issue codes relating to the knock sensor/s. If you discover any fault codes associated with it, it is time to repair the wiring or replace the knock sensor. You should also inspect the spark plugs to ensure that you are using the correct spark plug type for your car engine. To find the correct spark plugs, see your maintenance manual.

You should examine and change the ignition timing if you have an older car or if the engine has adjustable ignition timing. Check your service manual to see if you have adjustable timing. If you are unfamiliar with altering timing, have a repair company handle it because the technique requires certain special gear. However, the best course of action is to have your car checked by a specialist for thorough diagnosis and repairs.

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What causes engine knocking?

Engine knocking, also known as detonation, is typically caused by the premature ignition of the air-fuel mixture in the engine cylinder. It occurs when the compressed air-fuel mixture ignites before the spark plug fires, leading to multiple flame fronts colliding and producing a knocking sound.

How do you fix a knocking engine?

Fixing a knocking engine depends on the underlying cause. It could involve using higher octane fuel, addressing ignition timing issues, replacing faulty spark plugs, ensuring proper engine cooling, or repairing damaged engine components. In severe cases, a mechanic may need to inspect the engine for more significant issues.

What is knocking in a petrol engine?

Knocking-in a petrol engine refers to the rattling or metallic sound produced when the air-fuel mixture combusts at the wrong time due to factors like low-quality fuel, excessive engine load, or improper ignition timing.

What does a knocking sound in the engine mean?

A knocking sound in the engine indicates the occurrence of detonation or pre-ignition, where the air-fuel mixture ignites spontaneously and not as intended. This knocking noise is a sign of potential issues that require attention to prevent engine damage.

Can knocking damage an engine?

Yes, knocking can damage an engine over time if left unaddressed. The repeated knocking events put extra stress on engine components, leading to increased wear and potential damage to the pistons, cylinder walls, bearings, and other vital engine parts.

Can a knocking engine be saved?

The ability to save a knocking engine depends on the severity of the problem and how quickly it is addressed. In some cases, simple fixes like using the correct fuel or adjusting the ignition timing can resolve the issue. However, if the knocking is due to significant internal damage, it may require extensive repairs or even an engine replacement.

Can too much oil cause knock?

Yes, too much oil in the engine can cause knocking. When there’s an excessive amount of oil, it can create excessive pressure on the crankshaft and connecting rod bearings, leading to engine knocking.

Can spark plugs cause engine knock?

Yes, faulty or incorrect spark plugs can cause an engine knock. If the spark plugs are not functioning correctly, they may ignite the air-fuel mixture at the wrong time, contributing to engine knocking.

Do I need a new engine if it’s knocking?

Not necessarily. Whether you need a new engine depends on the severity of the knocking and the extent of the damage. In some cases, engine knocking can be resolved with repairs or adjustments. However, if the damage is significant and beyond repair, a new engine may be necessary.

That is all for this article, where we’ve discussed a lot about engine knocking. Nonetheless, the answers to the following questions were covered:

  • What is engine knock?
  • Why is an engine knocking?
  • Is it safe to drive if I hear an engine knocking?
  • What should you do if your car engine is knocking?

Hope you learn a lot from the reading. If you do, kindly share it with others. Thanks for reading; see you around!

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