What are the causes of engine knocking?

Engine knocking, also known as detonation, occurs when fuel burns unevenly in the cylinders, causing uncontrolled explosions. The primary causes include using low-octane fuel, carbon deposits, incorrect ignition timing, overheating, or a faulty knock sensor. Low-octane fuel ignites too early under compression, while carbon buildup increases compression ratios. Ignition timing issues can lead to premature combustion, and overheating raises cylinder temperatures. A failing knock sensor fails to adjust engine parameters to prevent knocking.

To diagnose and resolve engine knocking:

1. Use the recommended octane rating for your vehicle. Most modern cars require 95 RON or higher.
2. Clean carbon deposits with fuel additives or a professional decarbonisation service.
3. Check ignition timing and ensure spark plugs are in good condition.
4. Monitor coolant levels and thermostat function to prevent overheating.
5. Replace a faulty knock sensor if the engine control unit isn’t detecting knocking.

Ignoring knocking can damage pistons, cylinder walls, or bearings. If the issue persists, consult a mechanic to avoid costly repairs.

The reasons for engine knocking in cars are as follows:

Ignition timing too advanced: To ensure the piston receives power immediately upon entering the power stroke after the compression top dead center, ignition usually occurs before the piston reaches top dead center. However, excessively advanced ignition causes most of the fuel-air mixture to burn while the piston is still in the compression stroke. The remaining unburned mixture then undergoes extreme pressure and spontaneously ignites, resulting in knocking.

Excessive carbon buildup in the engine: Heavy carbon deposits in the combustion chamber not only increase the compression ratio (generating high pressure) but also create hot spots on the carbon surface, leading to engine knocking.

Overheating engine: An engine operating in excessively hot conditions, causing high intake air temperatures, or poor coolant circulation can result in high engine temperatures and knocking.

Incorrect air-fuel ratio: An overly lean fuel-air mixture raises combustion temperatures, which in turn increases engine temperature, making knocking more likely.

Low octane rating of fuel: The octane rating indicates a fuel's resistance to knocking. Higher octane fuels have greater anti-knock properties. Engines with high compression ratios have higher combustion chamber pressures, making them more prone to knocking if low-octane fuel is used.