What are the manifestations and causes of engine knocking?
3 Answers
Manifestations of engine knocking: You can clearly feel abnormal engine noise and vibration, which reduces engine output power, increases temperature, and raises fuel consumption. The specific reasons are as follows: 1. Excessive carbon deposits in the engine combustion chamber: Excessive carbon deposits in the engine combustion chamber not only increase the compression ratio (generating high pressure) but also create high-temperature hot spots or sparks on the carbon deposits, leading to engine knocking. 2. Overheating of the engine: If the engine operates in an excessively hot environment, causing high intake air temperature, or if the engine cooling water circulation is poor, it can result in engine overheating and knocking. 3. Low octane rating of the fuel: The higher the fuel grade, the stronger its anti-knock performance. Engines with high compression ratios have higher pressure in the combustion chamber. If fuel with low anti-knock performance is used, knocking is more likely to occur.
I remember my car suddenly made a metallic knocking sound during high-speed acceleration, like a hammer striking, with weak acceleration, soaring RPM but no increase in speed, and severe engine vibration. After checking for a long time, I realized it was engine knocking, which usually occurs under high load, such as when climbing or accelerating hard. The main reasons are fuel with too low an octane rating—I had filled up with cheap gas causing uneven combustion of the air-fuel mixture; or ignition that was too early, indicating a problem with the ignition system; excessive carbon deposits can increase the compression ratio, also leading to knocking. Knocking not only wastes fuel, increasing consumption by over 15%, but also damages engine components, potentially causing long-term harm to pistons and cylinders. Later, I switched to higher-octane gasoline and regularly cleaned the throttle body and combustion chamber carbon deposits, and the knocking disappeared, making driving worry-free and safe again.
The engine knocking sound is very noticeable. During test drives, I often hear customers complaining about that rattling piston slap, especially during startup or acceleration. The car lacks power, fuel consumption is significantly higher than normal, and sometimes there's slight black smoke. There can be multiple causes: poor gasoline quality with low octane leading to unstable combustion; ignition that's too early or system malfunctions triggering knocking; carbon deposits narrowing the combustion chamber and increasing compression ratio; overly lean air-fuel mixture or oxygen deficiency, such as from a clogged air filter. These can all lead to knocking, damaging valves and cylinder walls. I'd advise the owner to promptly change the oil, clean carbon deposits, and check ignition timing to prevent minor issues from becoming major headaches. Regular maintenance is key - like performing system checks every six months to ensure proper air-fuel mixture ratios.
