What are the causes of engine knocking?
3 Answers
The causes of engine knocking are: 1. Carbon deposits in the combustion chamber; 2. Using gasoline with an octane rating that is too low; 3. Poor quality gasoline; 4. Incorrect ignition timing. Symptoms of knocking: 1. Knocking creates sudden shock waves inside the cylinder that impact in all directions, causing strong vibrations in the engine's pistons, cylinder walls, connecting rods, crankshaft, etc., resulting in irregular metal knocking sounds; 2. Overheating of the cooling system; 3. Incomplete fuel combustion, with black smoke in the exhaust. Solutions: 1. Reduce the ignition timing advance; 2. Use gasoline with the specified octane rating; 3. Remove carbon deposits from the combustion chamber; 4. If knocking occurs when the car is going uphill, promptly shift to a lower gear; 5. Do not shift into a forward gear too early when starting the car.
I ran into this issue last time, there was always a metallic knocking sound during acceleration. Detonation, to put it simply, is abnormal combustion inside the engine, and the most frustrating part is using low-octane gasoline. Like my turbocharged car, it has a very high compression ratio and must run on premium 95 octane or higher. But once I tried to save money and filled it with 92 octane, and that's when the trouble started. Carbon buildup is also a major culprit. When carbon deposits accumulate on the piston top, they act like heating elements, causing the gasoline to self-ignite before the spark plug fires. The mechanic at the repair shop showed me with an endoscope—the carbon layer was as thick as a coin. Abnormal water temperature is also to blame; issues with the cooling system can turn the combustion chamber into an oven. Detonation is really deadly—over time, it can even crack the piston. Now, I always check the octane rating with a magnifying glass when refueling.
After a decade of car repair, five main causes of engine knocking have been identified: Fuel issues top the list, where low octane rating or water contamination in gasoline can cause premature ignition; Second is severe carbon buildup in the combustion chamber - those black deposits act like hot irons, igniting the air-fuel mixture too early; Third is incorrect ignition timing, caused by faulty control units or aging distributors advancing the spark too soon; Fourth is excessive intake air temperature, particularly common in turbocharged vehicles or those with intake system leaks; Fifth is overzealous forced induction modifications - some young enthusiasts recklessly flash tuning programs, pushing cylinder pressures beyond the engine's design limits. The most straightforward way to diagnose these issues is by reading knock sensor data streams with a diagnostic tool. For older vehicles, an annual carbon cleaning is recommended.
