Common Causes of Abnormal Engine Noises in Volkswagen Bora

[PatrickRose]

The causes of abnormal engine noises include premature fuel injection, diesel leakage from the injector, piston impact on the cylinder wall, excessive piston ring side clearance, impact between the valve stem head and rocker arm, and engine misfire. The specific cause can be determined based on different noise conditions, as detailed below: Abnormal noise caused by rough engine operation, commonly known as "knocking sound." The phenomenon is characterized by strong noise at low speeds, audible clearly from a distance of over ten meters, accompanied by difficulty in starting. After the engine starts, it runs unevenly, and coolant consumption is rapid. This noise is caused by premature fuel injection and requires readjustment of the fuel injection timing. Engine noise has a certain pattern, sometimes knocking, sometimes backfiring, accompanied by unstable engine speed and intermittent emission of black smoke. This uneven noise is caused by diesel leakage from the injector. When this occurs, the injector should be serviced. The engine emits a "thumping" or "knocking" sound, especially noticeable at low speeds or sudden speed changes, accompanied by oil burning. This noise is caused by excessive clearance between the piston and cylinder wall, increasing piston impact on the cylinder wall during diesel engine operation. The solution is to replace the cylinder liner or piston. A "clanging" sound, similar to a small hammer lightly tapping an anvil, can be heard along the entire length of the cylinder block, becoming more pronounced during sudden speed changes. This is caused by excessive piston ring side clearance. The piston rings should be replaced, and if necessary, the piston as well. A "clicking" or "tapping" sound around the cylinder head cover, quieter when the engine is hot and louder when cold, does not disappear when fuel supply is stopped at low speeds. The main cause is excessive valve clearance, leading to impact between the valve stem head and rocker arm. The valve clearance should be adjusted. Exhaust gas flow shows obvious intermittency, accompanied by severe exhaust pipe vibration and clear engine noise. This is caused by engine misfire.