Engine Knock Most Common Causes And How To Fix

Why Does Engine Knock

Engine knock also known as spark knock occurs when the air-fuel mixture in the combustion chamber ignites spontaneously before the spark plug fires. This can be caused by factors such as low octane fuel, high engine temperatures, excessive carbon deposits or incorrect ignition timing.

Is Engine Knocking Normal

No, engine knocking is not normal and should be addressed promptly. It can be a sign of issues like low-quality fuel, incorrect ignition timing, carbon buildup or other factors. Ignoring engine knock may lead to serious damage over time, impacting performance and longevity. If you experience persistent knocking, it’s advisable to consult a mechanic to diagnose and resolve underlying problem.

What Are Most Likely Common Cause Of Engine Knocking

Low-Octane Fuel – Using fuel with an octane rating lower than recommended for your engine can lead to knocking

Ignition Timing Issues – Incorrect ignition timing can cause the air-fuel mixture to ignite prematurely, leading to knocking.

Carbon Deposits – Carbon buildup in the combustion chamber can create hot spots, triggering premature ignition.

Overheating – High engine temperatures can contribute to knocking, often due to inadequate cooling or cooling system issues.

Faulty Knock Sensor – A malfunctioning knock sensor may fail to detect knocking and adjust the engine accordingly.

Incorrect Spark Plugs – Using the wrong type or worn-out spark plugs can affect combustion and contribute to knocking.

Excessive Exhaust Gas Recirculation – An improper functioning EGR system can cause a buildup of carbon deposit leading to knocking.

What Happens After Engine Knock

If engine knocking is not addressed promptly, it can lead to several potential consequences like :-

Engine Damage – Persistent knocking can cause damage to pistons, cylinder walls and other internal components of the engine.

Reduced Performance – Knocking negatively affects engine performance, leading to reduced power output, lower fuel efficiency and overall diminished vehicle performance.

Increased Wear – Continuous knocking can accelerate wear and tear on engine components, potentially shortening the engine’s lifespan.

Poor Fuel Economy – The inefficient combustion associated with knocking can result in poor fuel economy, coasting you more in fuel expenses.

Increased Emissions – Knocking can contribute to increased emissions, harming the environment and potentially causing a vehicle to fail emissions tests.

Expensive Repairs – Ignoring engine knock may eventually lead to severe damage, requiring costly repair or even engine replacement

Diesel Engine Knocking Cause

In diesel engines knocking is often referred to as diesel knock or combustion knock. Common causes of diesel engine knocking are..

Low-Quality Fuel – Using low-quality diesel fuel with poor ignition properties can lead to knocking.

Incorrect Injection Timing – Timing issues with fuel injection, such as early or late injection can contribute to knocking.

Faulty Injectors – Malfunctioning fuel injectors may spray fuel unevenly or at the wrong time, causing combustion irregularities and knocking.

Cylinder Pressure Imbalance – Variations in cylinder pressure, often due to issues with compression or combustion can lead to knocking.

Excessive Carbon Deposits – Accumulation of carbon deposits in the combustion chamber can create hot spots and promote knocking.

Over-Fueling – Providing an excessive amount of fuel to the combustion chamber can lead to incomplete combustion and knocking.

Poor Air-Fuel Mixture – Inadequate mixing of air and fuel in the combustion chamber can result in uneven combustion, causing knocking.

Petrol Engine Knocking Cause

In petrol or gasoline engines, knocking is often referred to as spark knock. Common causes of petrol engine knocking include..

Low-Octane Fuel – Using fuel with an octane rating lower than recommended for the engine can lead to premature combustion and knocking.

Incorrect Ignition Timing – Timing issues in the ignition system, such as advanced ignition timing can cause the air-fuel mixture to ignite too early resulting in knocking.

Carbon Deposits – Carbon buildup on the piston crown, cylinder walls or spark plugs can create hot spots that lead to knocking.

High Engine Temperature – Elevated engine temperature often due to cooling system issues or insufficient cooling can contribute to knocking.

Incorrect Spark Plug Heat Range – Using spark plugs with the wrong heat range can affect combustion and contribute to knocking.

Excessive EGR – Problem with the exhaust gas recirculation system can lead to increased carbon deposits and knocking.

Engine Overload – Operating the engine under heavy load condition, especially in high ambient temperature can promote knocking.

How To Diagnose Engine Knock

Listen For Sound – Pay attention to any unusual sounds coming from the engine. Knocking often produce a distinct metallic noise during combustion.

Identify Conditions – Note when the knocking occurs, whether it’s under acceleration, at idle, during warm-up or under load. This can provide clues to the underlying issues.

Check Fuel Quality – Ensure you are using the correct octane fuel recommended for your engine. Low-quality or incorrect fuel can contribute to knocking.

Inspect Ignition Timing – Incorrect ignition timing can cause knocking. Check the timing according to the manufacturer’s specifications.

Examine Spark Plugs – Worn or fouled spark plugs can affect combustion. Inspect the spark plugs for signs of damage, carbon buildup or incorrect heat range.

Evaluate Engine Temperature – Overheating can lead to knocking. Check the cooling system for issues such as low coolant level, malfunctioning thermostat or faulty water pumps.

Check For Carbon Deposits – Excessive carbon deposits in the combustion chamber can create hot spots. Consider using fuel additives or cleaners to address carbon buildup.

Inspect EGR System – If your vehicle has an EGR system, check for proper function. Issues with the EGR system can contribute to knocking.

Scan For Fault Code – Use an OBD-II scanner to check for any engine fault codes. This can provide additional insights into potential issues.

Consult A Professional – If you’re unable to identify the cause or if the knocking persists, seek the expertise of a qualified mechanic.

How To Fix Engine Knocking

Fixing engine knocking involves identifying and addressing the root cause of the issue. Below are steps to help you resolve engine knocking.

Use High-Octane Fuel – Switch to a higher octane fuel to resist premature combustion and reduce knocking.

Adjust Ignition Timing – Verify and adjust the ignition timing to the manufacturer’s specification. Correct timing helps prevent knocking.

Replace Spark Plugs – Install new, correct gapped spark plugs of the recommended type to ensure proper combustion.

Clean Carbon Deposits – Use fuel additives or cleaner to remove carbon deposits in the combustion chamber, reducing the likelihood of hot spots that cause knocking.

Maintain Cooling System – Ensure the cooling system is functioning correctly to prevent overheating, a potential cause of knocking.

Inspect EGR System – If applicable, check the EGR system for proper function. Clean or replace components if needed.

Upgrade Knock Sensor – If the knock sensor is faulty, replace it with a new one to ensure accurate detection of knocking and proper adjustments.

Check For Mechanical Issues – Inspect for mechanical problems such as loose or damage components, worn bearings or other issues that could contribute to knocking.

Avoid Overloading – Operate the engine within recommended load limits to prevent overheating and excessive stress.

Perform Regular Maintenance – Stick to a routine maintenance schedule, including oil change, air filter replacement and other preventive measures to keep the engine in good condition.

Consult A Mechanic – If you’re unable to identify or resolve the issue, seek the assistance of a professional mechanic. They can perform a comprehensive diagnosis and recommend specific repairs.


Addressing engine knocking promptly is crucial to prevent potential damage and ensure optimal engine performance. It’s always preferable to consult with a professional mechanic.

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