Engine detonation: causes and remedies
What is engine knock?
In some cases, the air / fuel mixture ignites before the spark plugs produce a spark. This phenomenon, accompanied by shock combustion of fuel, is the detonation of the engine. The huge combustion rate of fuel is associated with the ignition of the entire volume at the same time, and not sequentially from a spark. In addition, ignition starts earlier than the design crankshaft angle when the piston is still moving towards top dead center (TDC). The ignited gases expand rapidly, but the rising piston tends to compress them. As a result, the pressure in the combustion chamber is many times higher than the calculated value.
The shock wave from the mini-explosion (which, in fact, is the ignition of the fuel-air mixture) hits the walls of the cylinder and the bottom of the piston, which rises in the opposite direction to the gases. This shock generates sound waves, which the driver perceives as an unpleasant metallic knock or engine ringing.
Reasons for engine detonation:
The engine can detonate on any car: new, old, modern, or already out of production. It does not really matter the type of power unit, it is carbureted, or fuel injection is used.
On new cars, a special engine knock sensor is installed (only for injection power units). This device allows the on-board computer to regulate the operation of the motor so that it does not detonate.
Modern car engines operate at high compression ratios, so the risk that the air-fuel mixture will detonate is quite high. If the engine knock sensor is defective, the ECU cannot effectively regulate the unit. Problems will not keep you waiting.
The most common causes of engine detonation during acceleration, at rpm, or at idle speed are:
• fuel of poor quality or with an unsuitable octane number,
• too large an ignition lead,
• lean air-fuel mixture,
• carbon deposits on the cylinder walls,
• poor quality or unsuitable spark plugs,
• overheating of the engine due to a malfunction of the cooling system.
Fuel with an unsuitable octane rating or poor quality
If gasoline with an octane rating lower than the recommended one gets into the engine, detonation occurs with almost 100% probability. The car manufacturer calculates the compression ratio for a certain type of fuel, therefore the use of low-quality or unsuitable fuel in terms of octane number leads to engine detonation at idle or during acceleration.
Are you consciously buying gasoline with an octane rating lower than the one recommended by the engine manufacturer? This will cause the engine to detonate sooner or later. Trying to save money, you can find yourself in a very expensive repair.
It happens that refueling at an unchecked gas station becomes the cause of engine detonation. Make sure that the octane number of the flammable liquid that you fill in the tank of your car corresponds to the value recommended by the manufacturer. If you suspect a non-conformity, drain the questionable fuel. Use a proven gas station.
You can also improve the quality of the fuel with the “Maxxrecovery” Benzin Additive “Octane Plus”
Incorrectly configured ignition
In an effort to increase torque, some craftsmen change the factory settings of the ignition system. If the lead angle is set too large, the spark plug will spark before the piston approaches TDC. Ignition will occur ahead of time, when the fuel is not completely mixed with the air.
If engine detonation appears after an attempt to adjust the ignition angle, then the reason is the wrong setting. Even the masters in the auto repair shop can make mistakes, the more an error is possible with unskilled intervention.
Contact only trusted technical centers and be very careful about advice to change the ignition timing. It is better not to touch the settings of the manufacturer’s factory at all, if there is no complete certainty that they have gone astray.
Sometimes the reason for the detonation of a VAZ engine or another car brand is faulty spark plugs or unsuitable spark plugs. In this case, the spark may not be generated as expected by the motor manufacturer. Failure to spark a spark plug is one of the common causes of air / fuel ignition problems.
If your car’s engine detonates after replacing the spark plugs, check if they match the manufacturer’s recommended parameters. If the characteristics do not fit, replace with the corresponding product.
Lean fuel / air mixture
In pursuit of economy, motorists can deliberately deplete the air-fuel mixture. This is another reason why engine knocking occurs. Due to insufficient concentration of fuel vapors, the spark cannot ignite the mixture. At the next injection cycle, on the contrary, the fuel vapor becomes more than normal. An overly rich mixture ignites prematurely from compression
Carbon deposits on cylinder walls
Often the cause of engine detonation at rpm is the presence of deposits on the inner surface of the combustion chamber. Carbon deposits heat up and act as a wick, igniting the air-fuel mixture. In addition, carbon deposits increase the compression ratio and fuel with a given octane number ignites earlier due to the increase in compression temperature.
If the power unit continues to operate for up to 20 seconds with the ignition off, then carbon deposits have accumulated on the cylinder walls. Often these deposits heat up and act as a wick, causing the air-fuel mixture to self-ignite even in the absence of a spark from the spark plugs.
To prevent this phenomenon, it is recommended to regularly, at least 2 times a year, apply the Maxxrecovery “Clean & Protect Advanced” additive for gasoline engines.