Warning! If you have the slightest doubt about self-diagnosis, get out the tow rope. Serious repairs to a damaged engine will cost more than the services of a tow truck.
Knocking of main bearings (can be heard at the very bottom of the cylinder block) - very dangerous; stop the engine immediately, you will have to tow it to a car service or garage. A low-pitched knock, noticeably increasing under load and with an increase in crankshaft speed. Often its appearance is accompanied by a drop in oil pressure (the emergency oil pressure drop warning light is on almost constantly).
Knocking of connecting rod bearings (heard in the middle of the cylinder block) - very dangerous; stop the engine immediately, you will have to tow it to a car service or garage. The sound is rhythmic, ringing, metallic, medium tone. It increases significantly with increasing load and completely disappears when the spark plug is disconnected.
Knocking of piston pins (can be heard in the upper part of the cylinder block) - dangerous; without loading the engine, you can drive to the car service or garage yourself. Rhythmic, high-pitched with a sharp metallic tint, heard in all engine operating modes, increases with increasing engine load. Completely disappears when the spark plug is disconnected.
Knocking of worn pistons and cylinders (can be heard in the same part of the engine as the knocking of piston pins) – harmless; without putting too much load on the engine, you can drive to the car service or garage yourself. A sound reminiscent of the clatter of clay pottery. It is especially audible on an unheated engine, and decreases or disappears as it warms up.
Valve knocking (can be heard in the upper part of the engine in the area of the cylinder head cover) – not dangerous; you can drive to a car service or garage yourself. Metallic knocking against the background of a general dull noise. It is clearly audible at low and medium crankshaft speeds from the cylinder head side above the valve locations.
Detonation knocks dangerous, but are usually eliminated by replacing the knock sensor or refueling with high-quality fuel. Avoiding heavy engine load, you can drive to a car service or garage yourself. Ringing metallic knocks that usually occur when accelerating the car. The cause is a failure of the knock sensor, the use of low-octane fuel, engine overload when engaging a high gear too early, significant carbon formation in the combustion chambers. It is necessary to use a special fuel additive to remove carbon deposits on the valves and combustion chambers.