Knocking "fingers" during acceleration: the main reasons. Troubleshooting rules

Any extraneous noise in the engine of the car often cause the owners a sense of alertness. And even if these sounds do not affect the driving performance, their very appearance makes the driver think about the diagnosis. On many cars, the "fingers" are tapping during overclocking, but this problem is often ignored. The sound appears when the car is picking up speed. If you do not pay attention to it in time, there are much more serious problems. At the same time to determine the reasons for the occurrence of knocking, and also to fix this problem motorists can not independently. Let's look at the reasons for these unpleasant driver's ear sounds, and also learn how to eliminate these problems with the motor.

Knock of fingers

From the engine, which works under load, can be heard ringing metallic sounds. They disappear when typing a certain speed. The mechanics of the old school will say that they are tapping "fingers" during the dispersal. However, the driver will be surprised, and will be completely right: to the "fingers" installed in the pistons, the sound has nothing to do. The nature of this knock is of a different nature. It is caused by detonation. Sometimes, for certain reasons, fuel can burn incorrectly. The blast wave in the combustion chamber is reflected from the piston and from the walls of the cylinder. At the same time, the loudest metallic knocking is created, in which specialists hear the sound of "fingers".

Why "fingers"?

The process of combustion of a combustible mixture in a fully serviceable motor goes successively. A spark ignites near the spark plug, and gradually it fills the entire cylinder. But there is another variant of combustion - detonation. Explosion of the fuel mixture in the combustion chamber occurs abruptly. This increases the pressure and temperature. This very explosion is called detonation. That's why the driver hears a knock - it comes from a blast wave. Proper combustion means the speed of fire spread to 30 m / s. The pressure of the gases increases gradually. With this combustion, the flame fills the cylinder gradually. The gases press the piston gently. There are no thuds of gas on the walls of the combustion chambers, since there is no explosion. If the burning rate is greater, then this is the prerequisite for detonation. By the way, this phenomenon is very harmful for the engine.

Detonation - what is it?

If the "knuckles" are tapping during acceleration, this indicates a detonation in the engine. This is called instantaneous and very destructive in its strength explosion of any inflammable substances after impact or detonator operation. This definition is from Ushakov's dictionary. Detonation of combustible substances for car engines is a rapid burnout of a mixture of gasolines and air. It occurs when the engine is running under load at low rpm and low-quality fuel. This process is accompanied by knocking, vibration, rising temperature. As a result, tapping "fingers" during acceleration (VAZ-2112 including).

Why does detonation occur?

The octane number of fuel is an indicator that characterizes the coefficient of resistance of a combustible liquid to ignition during compression. In other words, it's detonation resistance. Naturally, the engines, where the compression ratio is high enough, requires fuel with a high octane number. Any modern engine has a high compression ratio. If you fill it with low-octane gasoline, this greatly increases the risk of detonation. Caliber ignition is the independent combustion of a fuel mixture in cylinders. One of the reasons for this phenomenon is unburnt soot or high temperatures in the combustion chamber. Another reason why the "thumbs" are knocking on the engine during acceleration is a poor fuel mixture. If you increase the amount of air in relation to the volume of fuel, it causes detonation. Too poor mixture at the time of hitting the cylinder will cause detonation with greater probability than normal. Also, this effect occurs at high loads. Tapping "fingers" on the acceleration is precisely because of the overload of the power unit. If you start to move in the third gear instead of the first, you may not only have a ringing, but also a characteristic metallic clang.

More about the reasons for the knock

When the car picks up speed, for the engine it's a stressful situation. Especially if you need to disperse the car suddenly. When the driver squeezes the accelerator pedal into the floor for a sharp set of revolutions, for example, from one to six thousand, then the driver will hear how the "fingers" are tapping during acceleration ("Priora" is no exception). It's quite normal. To quickly gain speed, the electronics feeds more cylinders with the same amount of air, which will uniquely lead to the appearance of detonation. But also the situation is possible and on smooth starts. The driver will hear a characteristic knock. This phenomenon is not normal with a smooth set of speed. In these cases, it is necessary to quickly identify and eliminate the cause. This will help to avoid trouble.

Typical reasons for ringing "fingers" during normal operation of ICE

If the "fingers" are tapping during the dispersal in the "Kalina", the DMRV may have failed. If it does not work correctly, then the ECU will receive incorrect information and give the wrong commands. Another reason is that the ignition timing is incorrect . For this reason, the point at which the fuel will burn as much as possible is near TDC. This leads to an increased pressure in the combustion chamber. If the "fingers" are tapping during acceleration on the Ford Focus, the knock suppression sensor may have failed. Be sure to check this item. If it ceases to work, it should be replaced. Low-quality fuel is the cause of all troubles that happen to cars. This has already been described in detail above. It should be noted that knocking your fingers is not always a problem that was formed during the use of the car. There are situations when the machine is already coming from the factory with incorrectly connected sensors. As a result, this leads to detonations and knocking. This problem is especially dangerous, because the engine is on the break-in and detonation is especially harmful to it. It should be deleted.

Effects

Detonation can cause irreparable consequences for the engine. This burnout and other damage to the valves, breakage of the piston rings. At this point, the engine experiences enormous thermal and mechanical loads. The edges of the pistons melt, the bridges between the rings break. Also gets and connecting rod inserts.

How to avoid detonation?

All without exception, modern cars are equipped with a special sensor and a block that react and suppress this destructive phenomenon. As soon as detonation occurs, the sensor's membrane captures the voltage, the magnitude of which depends on the frequency and on the amplitude of the blast wave in the cylinder. The executive system receives the signal from the sensor and changes the algorithm of the ignition system. If you hear "fingers" when accelerating ("Tavria"), the causes of this phenomenon can be in gasoline, carburettor tuning, ignition angle. The easiest way to avoid detonation is to prevent premature ignition. You can also increase the engine speed. When running, it is recommended to increase the speed smoothly. If you need a sharp start, then experts recommend to unscrew the motor before the start, and then start moving. To reduce detonation, you can use the method of selecting the calylic number of candles. In this case, it is recommended to use hotter candles. They will burn the entire fuel mixture without residue, and there will be no turbulence.

Conclusion

Detonation always occurs unexpectedly and can greatly frighten car owners. When the fingers "knock", it is worth using these recommendations, the reasons are described in detail. If the problem can not be solved independently, then it is worth asking for help in SRT.