What Causes Engine Knock in Cars?

[DallasRose]

Car engine knock is caused by: 1. Excessively advanced ignition timing: When ignition occurs too early during the compression stroke, most of the air-fuel mixture burns while the piston is still compressing, causing the remaining unburned mixture to auto-ignite under extreme pressure, resulting in knock. 2. Severe carbon buildup in the engine: Excessive carbon deposits in the combustion chamber not only increase the compression ratio but also create hot spots on the carbon surface, leading to engine knock. 3. Overheating engine: High intake air temperatures in hot environments or poor engine coolant circulation can both cause high-temperature engine knock. 4. Incorrect air-fuel ratio: An overly lean fuel mixture raises combustion temperatures, which increases engine temperature and makes knock more likely to occur.