Reasons Why Is Your Engine Knocking: Causes and Fixes

“Engine knocking” refers to the distinct pinging or tapping sound that emerges from the engine of your vehicle. As the usual smooth running noise of your engine converts into knocking, scraping, or tapping, it’s a clear indicator of potential issues within your engine.

Reasons For Engine Knocking

Encountering engine knocking noise is a concerning situation, as it has the potential to inflict significant harm to the engine. 

The sound of an engine knock is something to be avoided, as it can lead to the failure of different internal engine parts. Fortunately, addressing a knocking engine often involves relatively straightforward repair measures. This article explains the engine knocking reasons and how to fix them.

What is an Engine Knock?

Engine knocking is the result of uneven fuel combustion within the engine cylinder. When the air-fuel mixture is properly balanced, combustion occurs in controlled pockets rather than simultaneously.

Each combustion pocket generates a small shock that triggers the ignition of the next pocket, and this cycle continues. However, if fuel doesn’t burn properly, these shocks can be mistimed, leading to the occurrence of engine knocking.

Causes of Engine Knock

Low octane fuel and incorrect ignition timing are the most common causes of engine knocking. However, it can also be caused by the wrong spark plug, lean air-fuel mixture, worn bearings, or a serpentine belt.

These causes of the engine knock are discussed deeply below:

1) Low Octane Fuel

Fuel Octane Rating

Engine knocking during acceleration is most commonly caused by using low-octane or dirty fuel. This situation can arise due to either mistakenly choosing the low-octane fuel type at the gas station or receiving subpar fuel from the station itself.

When the wrong fuel enters the combustion chamber of your engine, it can trigger early burn, resulting in engine knocking.

If this problem emerges after refueling, a potential solution is the use of an octane booster. This additive can elevate the octane level of your fuel, mitigating knocking without necessitating a complete fuel replacement.

2) Damaged Crankshaft 

Damaged Crankshaft

In the engine, the piston rings perform vertical movements within the engine cylinder linked to the crankshaft. The motion of the crankshaft is controlled by the engine timing system. The bearings and connecting rod that connect the engine cylinder to the crankshaft play a crucial role in upholding the correct gap between them.

If the crankshaft undergoes damage, leading to improper clearance between the cylinders, it can result in a metal-on-metal impact known as a “rod knock.”

3) Incorrect Ignition Timing

Incorrect Ignition Timing, causes of knocking sound

An excessively advanced ignition timing may also lead to engine knocking or pinging noise. Consequently, a bad ignition timing could indeed be responsible for the occurrence of engine knocking.

This issue usually occurs in older vehicle models equipped with adjustable ignition timing through means such as a distributor, adjustable camshaft sensor, or adjustable crankshaft position sensor.

However, modern vehicle models rely on electronic control for ignition timing, rendering manual adjustments unfeasible.

For old models featuring adjustable ignition timing, the timing check demands an ignition timing light. To lessen engine detonation, a slight timing retardation can be helpful. However, adhering to the repair manual’s guidance for accurate ignition timing adjustments is strongly advised.

4) Lean Air-Fuel Mixture

It is possible that you don’t know it, but the fuel that enters the combustion chamber not only powers combustion but also helps to cool the combustion chamber. When the air-fuel mixture becomes too lean, its cooling effect reduces, leading to excessive heat buildup within the combustion chamber.

This excessive temperature may lead to the premature ignition of the fuel-air mixture, occurring before the spark plug has a chance to ignite it. This issue leads to engine knocking. Such situations pose risks to the engine’s internal parts and can accelerate the deterioration of pistons and fuel injectors.

5) Faulty Knock Sensor

Knock Sensor

A faulty knock sensor is also one of the most common causes of engine knocking. The primary function of your vehicle’s knock sensor is to safeguard the engine against knocking occurrences.

To ensure optimal performance, the powertrain control module (PCM) aims for advanced ignition timing. When lower octane fuel is added to your fuel tank, the engine needs a more conservative ignition timing to avert knocking.

The knock sensor plays a vital role by constantly monitoring for any knocking events. Upon detection of such an event, it sends a command to the engine to further adjust and retard the ignition timing, preventing potential engine harm.

However, when the knock sensor becomes faulty, it may send inaccurate information to the PCM, leading to the engine knock.

6) Stretched-Out Serpentine Belt 

serpentine belt

The vehicle contains a serpentine belt that further drives different accessories of the vehicle. It is powered by the vehicle’s engine.

When the engine starts operating, it drives the serpentine belt that’s linked to various pulleys responsible for powering different engine accessories. This belt needs to maintain optimal tension for seamless and quiet rotation.

If the belt becomes too stretched, it loses the right tension, leading to noises like squealing, clicking, or rattling. These sounds might be mistaken for typical engine sounds.

Read More: Bad Serpentine Belt Symptoms and Causes

7) Wrong Spark Plugs

Bad Spark Plug

While it’s relatively uncommon, using an incorrect spark plug may indeed lead to engine detonation or knock.

Spark plugs play a vital role by providing the precise ignition spark needed to ignite the fuel/air mixture. Spark plugs are available in different types designed for special vehicle models. Therefore, installing the wrong type can potentially trigger knocking issues in your engine.

In one scenario, the spark plug might fail to generate sufficient spark, or the spark might be too feeble. To prevent this, it’s essential to consult your vehicle’s service manual to identify the appropriate spark plug type for your specific car model.

Read More: Bad Spark Plug Symptoms and Causes

8) Worn Bearings 

Connecting rod Bearings

Over time, the bearings on the connecting rod between the crankshaft and the cylinders may lead to the rod knock.

With time, your engine accumulates contaminants such as grime, dirt, and carbon deposits. These substances can gather at the rod bearing’s back, leading to the connecting rod damage. When the connecting rod is damaged, the usual motion of the rod is replaced by undesirable sounds like knocking or piston slaps.

9) Non-Lubricated Cylinder Head 

Proper lubrication is essential for all engine cylinders to function smoothly. If a cylinder operates without sufficient lubrication, it can produce a distinct knocking noise.

Lubrication issues often arise from engine oil leaks. Additionally, adding generic oils with lower flashpoints may lead to poor lubrication of the engine parts. To address this, many automakers suggest the use of synthetic engine oil for effectively lubricating the cylinder head.

Insufficient lubrication of the cylinder head may also lead to the cylinder wall and piston ring damage, potentially causing a piston slap—a problem that necessitates prompt correction.

As you detect oil leaks, it’s advisable to position an oil pan beneath the car to catch any escaping engine oil before changing your oil.

10) Low Coolant

coolant level, reasons of engine knock

When the vehicle engine starts to experience a depletion of coolant, it can lead to overheating, accompanied by knocking or pinging noise. The primary causes of low coolant are various factors such as radiator damage, hose leaks, or blown head gasket.

Coolant within your engine can inflict significant harm on the bearings as it mixes with the engine and weakens its ability to lubricate the engine parts. Furthermore, engine overheating has the potential to lead to complete engine failure.

Read More: Coolant Leak Symptoms and Causes

How to Fix Engine Knock

Follow the below-given steps to fix the engine knock:

  • Find the main issue of the engine knock before repairing any part.
  • Check the quality and condition of your fuel. If it is a low-quality fuel, change it with high-octane fuel recommended by your manufacturer.
  • Check the ignition timing and make the needed adjustments.
  • Inspect the spark plugs and replace the worn ones.
  • Remove the carbon deposits accumulated on the engine parts.
  • Adjust the valve clearance if needed.
  • Inspect the PCV valve and other components of the PCV system for signs of damage.
  • If your engine is overheating, find the main cause of overheating and make necessary repairs.
  • Check the oil level and condition. If the engine oil is insufficient, add more oil.
  • Inspect the knock sensor for a fault. If the sensor is faulty, replace it promptly.
  • Conduct a compression test for the internal engine problems.
  • If you won’t be able to fix the engine knocking, conduct a professional is recommended.

FAQ Section

What does the Engine Knock mean?

Engine knocking is the result of uneven fuel combustion within the engine cylinder. Encountering engine knocking noise is a concerning situation, as it has the potential to inflict significant harm to the engine.

What does Engine Knock Sound like?

Engine knock resembles the noise of striking your engine block with a metal hammer and is particularly noticeable while driving. When this knocking sound becomes louder as you increase the speed of your engine, it’s expected a case of engine pinging or knocking.

Can I drive my car with a knocking engine?

Yes, it is possible to drive with a knocking engine, but it is strongly discouraged. Driving with engine knock poses significant risks to sensitive and costly parts of your engine, potentially leading to repair expenses exceeding $4000 if not handled cautiously.

How can I stop the engine knocking?

To address engine knock, it is important to find and address the main issue. Knocking noise is most commonly produced due to wrong octane fuel, faulty serpentine belts, insufficient lubrication, low coolant levels, or engine overheating. To fix it, start by ensuring that your fuel possesses the appropriate octane rating for your specific car model. Using an octane booster may potentially reduce the sensitivity to detonations.

Can low oil cause engine knock?

Yes, low engine oil doesn’t directly influence ignition timing or engine knock. But it can indirectly cause engine knocking if oil levels are extremely low, leading to insufficient oil pressure.

How much does it cost to fix an engine knock?

The cost to fix an engine knock depends on the underlying issues. You may need to add the octane boosters, replace the knock sensor, adjust ignition timing, or even refill the fuel tank. Generally, the estimated cost to fix engine knock ranges between $80 to $220.

What is a Carbon Deposit?

During the combustion of the air-fuel mixture, carbon sludge is produced, which is known as the carbon deposit. These deposits start to accumulate mostly inside the engine cylinder. This accumulation of carbon has the potential to obstruct cylinders, as well as parts like fuel injectors or air filters, thereby potentially elevating compression within the combustion chamber.

Leave a Comment