What are the causes of engine detonation and how to fix it

Engine detonation – causes and consequences

Engine detonation can lead to significant wear of such engine parts as the cylinder-head gasket, elements of the cylinder-piston group, pistons, cylinders and other parts. All this significantly reduces the life of the power unit up to its complete failure. If this harmful phenomenon occurs, it is necessary to diagnose the cause of detonation and get rid of it as quickly as possible. How to do this and what to pay attention to – read below.

What is detonation

Detonation is a disturbance in the combustion of the fuel mixture in the combustion chamber, when combustion occurs not smoothly, but explosively. In this case, the velocity of propagation of the blast wave increases from the standard 30…45 m/s to supersonic 2000 m/s (exceeding the speed of sound by the blast wave is among other things the cause of the clap). In this case, the fuel-air mixture explodes not from the spark coming from the spark plug, but spontaneously, from the high pressure in the combustion chamber.

Naturally, the powerful blast wave is very harmful to the cylinder walls, which overheat, pistons, cylinder-head gasket. The last one suffers the most, and in the process of detonation the explosion and high pressure burn it out (in slang it is called “blowing out”).

Detonation is inherent in engines operating on gasoline (carburetor and injector), including those equipped with gas equipment (HBO), that is, operating on methane or propane. However, it occurs more often in carbureted cars. Diesel engines operate under a different scheme, and there are other causes of this phenomenon.

Causes of engine detonation

As practice shows, detonation occurs most often on old carburetor engines, although in some cases, this process may occur and on modern injector engines equipped with an electronic control unit. Some of the reasons detonation can occur include:

• Excessively depleted fuel-air mixture . Its composition can ignite before the spark reaches the combustion chamber. In this case, high temperatures provoke oxidation processes, which cause an explosion, i.e. detonation.
• Earlier ignition . If the ignition angle is too high, the ignition of the air-fuel mixture begins before the piston reaches the so-called top dead center.
• Use of unsuitable fuel . If gasoline with a lower octane rating than that prescribed by the manufacturer has been poured into the car tank, there is a high probability that detonation will occur. This is explained by the fact that low-octane gasoline is more chemically active and reacts chemically faster. A similar situation will occur, if instead of quality gasoline some substitute like condensate is poured into the tank.
• High compression ratio in the cylinders . In other words, coking or other contamination in the engine cylinders, which gradually accumulates on the pistons. And the more fouling there is in the engine, the higher the probability of detonation in the engine.
• Faulty engine cooling system . The fact is that if the engine overheats, the pressure in the combustion chamber can increase, and this in turn can cause detonation of the fuel in the appropriate conditions.

The detonation sensor is like a microphone.

These are common causes for both carbureted and injector engines. However, an injector engine may have another cause: a detonation sensor failure. It sends appropriate information to the ECU about the occurrence of this phenomenon and the control unit automatically changes the ignition angle in order to get rid of it. If the sensor fails, the ECU will not do this. In this case, the Check Engine light will activate on the dashboard, and the scanner will display an engine detonation error (diagnostic codes P0325, P0326, P0327, P0328).

Currently, there are many different options for ECU reprogramming in order to reduce fuel consumption. However, using them is not the best solution since there are cases when such firming led to unfortunate consequences, in particular to incorrect work of detonation sensor, i.e. the engine control unit simply cut it off. Accordingly, if detonation does occur, the sensor does not report it and the electronics do nothing to eliminate it. Also in rare cases the wiring from the sensor to the ECU may be damaged. In this case the signal also does not reach the ECU and a similar situation occurs. However, all these errors can be easily diagnosed with an error scanner.

There are also a number of objective factors that influence the occurrence of detonation in individual engines. Specifically:

• Engine compression ratio. Its value is due to the peculiarities of the ICE design, so if the engine has a high compression ratio, it is theoretically more prone to the occurrence of detonation.
• The shape of the combustion chamber and the bottom of the piston. This is also a design feature of the motor, and some modern small in volume but powerful engines are also prone to detonation (but their electronics control this process and detonation in them is a rarity).
• Forced engines. They usually have high combustion temperatures and high pressure, so they are also prone to detonation.
• Turbocharged engines. Similarly to the previous point.

As for detonation in diesel engines, the reason for its occurrence may be the angle of advance of fuel injection, poor quality of diesel fuel, problems with the engine cooling system.

Also the cause of detonation may be the operating conditions of the machine. In particular the engine is more subject to this phenomenon under the condition that the car is moving in high gear, but with low speed and engine revolutions. In this case there is a high degree of compression, which can provoke the appearance of detonation.

Also some car owners are trying to reduce fuel consumption, and for this re-flash the ECU of their cars. However, this may lead to a situation where a lean fuel-air mixture reduces the dynamics of the car, increasing the load on the engine, and at higher loads, there is a risk of detonation of fuel.

What causes are confused with detonation

There is such a concept called “glow ignition”. Many inexperienced motorists confuse it with detonation, because with glow ignition, the engine continues to run even when the ignition is off. In fact, in this case, the fuel-air mixture is ignited by heated engine components and it has nothing to do with detonation.

Another phenomenon that is mistakenly considered to be the cause of engine detonation when the ignition is off is called dithering. This behavior is characterized by a short operation of the engine after switching off the ignition at an increased compression ratio or the use of fuel that does not match the detonation resistance. This leads to spontaneous ignition of the air-fuel mixture. That is, the ignition occurs as in diesel engines, under high pressure.

Signs of a detonation

There are a number of signs by which you can indirectly determine that detonation occurs in the engine of a particular car. It is worth stating at once that some of them may indicate other breakdowns in the car, but it still makes sense to check the presence of detonation in the engine. So, the signs include:

• The appearance of a metallic sound from the engine when it is running . This is especially true when the engine is running under load and/or at high rpm. The sound is very similar to the one that occurs when two iron structures hit each other. This sound is exactly what is caused by the blast wave.
• A drop in engine power . Usually, the engine is not stable, may choke while idling (true for carbureted cars), it takes a long time to pick up revolutions, the car decreases its dynamic characteristics (it does not accelerate, especially if it is a loaded car).

Rokodil ScanX diagnostic scanner to connect to the ECU of a car

Here it makes sense to give signs of detonation sensor failure. Like in the previous list, the signs can indicate other breakages, but in injection machines it is better to check the error with the electronic scanner (the most convenient way is to use Rokodil ScanX multimaster scanner, which is compatible with all cars from 1993 year and allows connecting to your smartphone with iOS and Android via Bluetooth). Such a device will allow you to see the detonation sensor and other indicators in real time.

So, the signs of detonation sensor failure:

• Unstable engine operation at idle speed;
• decrease of engine power and in general the dynamic characteristics of the car (weak acceleration, no traction);
• increased fuel consumption;
• Difficult engine start, at low temperatures it is especially noticeable.

In general, the signs are identical to those of late ignition.

Consequences of detonation

As indicated above, the consequences of detonation in the car engine are very serious, and in no case should be delayed the performance of repair work, because the longer you drive with this phenomenon – the greater the destruction of the engine and its individual elements. Thus, the consequences of detonation include:

• Combustion of the cylinder-head gasket . The material from which it is made (even the most modern), is not designed to work in conditions of high temperature and high pressure, arising in the process of detonation. Therefore it will fail very quickly. And a punctured cylinder-head gasket will lead to other troubles.
• Accelerated wear of elements of the cylinder-piston group . This applies to all of its elements. And if the engine is not new or has not been overhauled for a long time, it can end very badly, up to its complete failure.
• Breakdown of the cylinder head . This case is one of the most complicated and dangerous, but if you drive with detonation for a long time, its realization is quite possible.

Burned cylinder-head gasket.

Damage and destruction of the piston

• Burnout of the piston/pistons . In particular, its bottom, the lower part. It can often not be repaired and only needs to be replaced in its entirety.
• Destruction of the bridges between the rings. Under the influence of high temperature and pressure, they can be destroyed among the very first of the other parts of the engine.

Broken cylinder head.

• Bending of a connecting rod. It is similar here, under explosion conditions its body can change its shape.
• Burning of the valve poppets . This process happens very quickly and has unpleasant consequences.

As can be seen from the list, the consequences of the detonation process are the most serious, so you can not allow the engine to work in its conditions, respectively, the repair should be performed as soon as possible.

How to remove detonation and prevention methods

The choice of a method for eliminating detonation depends on the cause that caused this process. In some cases, to get rid of it, it is necessary to perform two or more actions. In general, the methods of combating detonation are:

• Using fuel with the parameters recommended by the car manufacturer. In particular, it concerns the octane number (do not underestimate it). It is necessary to fill up at the checked up gas stations and not to fill up the tank with any substitute. By the way, even some high-octane gasoline contains gas (propane or other), which unscrupulous producers pump into it. This increases its octane number, but not for long, so try to pour quality fuel into the tank of your car.
• Set a later ignition. Statistically, ignition problems are the most common cause of detonation.
• Perform a cracking, clean the engine, that is, make the volume of the combustion chamber normal, without soot and dirt. You can do it yourself in a garage, using special agents for cracking.
• Perform an inspection of the engine cooling system. In particular, check the condition of the radiator, sockets, air filter (replace it if necessary). Also do not forget to check the level of antifreeze and its condition (if it has not been changed for a long time, it is better to change it).
• It is necessary to set the advance angle of fuel injection in diesels correctly.
• Use your car correctly, don’t drive in high gears with low speed, don’t overproof ECU to save fuel.

As a preventive measure, you can advise to monitor the condition of the engine, periodically clean it, change the oil in time, perform anticarbon treatment, avoid overheating. Similarly, keep the cooling system and its elements in good condition, change the filter and antifreeze in time. One more trick is to periodically let the engine to work on high revolutions (but without fanaticism!), do it in neutral gear. In this case, under the influence of high temperature and load, various elements of dirt and debris fly out of the engine, that is, it is cleaned.

Detonation usually occurs when the engine is hot. In addition, it is more likely on engines that are operated at minimum loads. This is due to the fact that they have a lot of sludge on the pistons and cylinder walls with all the ensuing consequences. And usually the engine detonates at low revolutions. Therefore, try to run the engine at medium rpm and with medium loads.

It is worth mentioning about the detonation sensor separately. Its operating principle is based on the use of a piezo element, which converts the mechanical impact on it into an electric current. Therefore, it is easy enough to check its operation.

The first method is with a multimeter, working in the mode of measuring electrical resistance. To do this, you need to disconnect the chip from the sensor, and instead connect the stylus of the multimeter. On the screen of the device you will see the value of its resistance (in this case, the value itself is not important). Then with a wrench or other heavy object hit the bolt fixing the sensor (but be careful not to overdo it!). If the sensor is good, it will perceive the impact as a detonation and will change its resistance, which you can judge by the instrument readings. In a couple of seconds the resistance value should return to the initial position. If this does not happen, the sensor is defective.

The second method of checking is more simple. To do this, you need to start the engine and set its revolutions somewhere at the level of 2000 rpm. Open the hood and with the same key or a small hammer hit the sensor mount. Serviceable sensor should perceive it as detonation and inform the ECU about it. The ECU will then give a command to reduce the engine rpm, which you will clearly hear by ear. Similarly, if this does not happen, the sensor is defective. This unit can not be repaired and must only be replaced in its entirety, good thing it is not expensive. Pay attention that when you install a new sensor on its seat, you must ensure good contact between the sensor itself and its system. Otherwise, it will not work correctly.

Engine detonation: description of the process, causes of occurrence and troubleshooting methods

The importance of the correct functionality of the engine of a vehicle is essentially comparable to the role of the heart for the human body. Although all the nodes of the machine and work in absolute interaction, and each detail performs a fundamental role in its performance, the engine is assigned the main role – the driving force, without which the car will not function. The slightest malfunction of the engine should be the cause for concern to the car owner, the incentive to find the cause of failure and eliminate it immediately. In this article, we will talk about the phenomenon that motorists call detonation of the power unit, consider the causes of such a precedent and ways to eliminate it.

Detonation: a basic characteristic of the phenomenon

Before determining the causes of the precedent and looking for ways to solve the problem, it is worth understanding what engine detonation is and how a car owner can recognize it. Detonation, as a dangerous phenomenon for the engine, is most often manifested by uncharacteristic sounds from the unit. An annoying metallic knock, comparable to a microburst in reproduction, often occurs when the ignition is turned on, under load or when shutting down. Detonation at engine startup, when the unit is operating at idle speed, is perceived by many motorists as an ignition problem, but if the precedents appear in other situations, supplemented by secondary signs of detonation, the causes lie much deeper. Additional signs of detonation can manifest themselves in the following:

1. Rapid increase in fuel consumption.
2. Deterioration of unit power parameters.
3. Regular engine overheating.
4. Changes in the color of smoke from the exhaust pipe from almost transparent to black.

If the above symptoms are manifested in a complex and systematic manner, it means that the engine is subjected to detonation, which is a self-ignition of fuel in the combustion chamber, resulting in an explosion wave, negatively affecting the component parts of the unit.

Dangerous effects of detonation

Responsible and attentive drivers take effective action at the slightest, sporadic uncharacteristic sounds during power unit operation: letting the situation drift away can lead to serious problems such as major repairs involving substantial financial expenditure. Detonation of the unit is not the exception, but rather the rule in this situation, as an uncharacteristic sound of engine operation and increased fuel consumption is only the “tip of the iceberg” in such a problem. The improper combustion of the mixture in the cylinders, in addition to the sound explosive manifestation, is accompanied by the impact of the wave on the components of the unit in the form of vibration, destroying the engine from the inside. The consequences of engine detonation are as follows:

1. A radical decrease in the performance of the motor, the cause of which is the rapid wear of the elements of the crank and connecting rod series.
2. Destruction of pistons and internal walls of cylinders as a result of systematic overheating of the power unit.
3. Burning of the gasket of the engine block, located under the cylinder head.

As the final result of the destructive effect of detonation is an absolute engine failure, followed by a costly and time consuming repair.

The root causes of the precedent

Having understood the peculiarities of the concept of detonation, its practical destructive effect on the functionality of the motor, it is worth moving on to the search for factors that provoke such a phenomenon. There are many factors, as a result of which detonation can occur in the engine, although most of them are considered indirect, lead to negative consequences in a complex effect. The causes of engine detonation are identical for all types of power units, often consisting of the following:

1. Fuelling with low-octane fuel or fuel of poor quality.
2. Coking the engine with combustion components.
3. Operation of spark plugs that do not meet the car manufacturer’s requirements.
4. Malfunctions of the mixing process.
5. Overheating of the power unit.
6. Malfunction of the engine cooling system.
7. Malfunction of injectors or fuel pump.

Each of these factors can become the primary source of detonation, provoking additional problems in the ignition of the fuel mixture, which will result in the incorrect functioning of the engine. When detonation occurs, it is important to understand what is happening in the engine, to determine the exact source of the problem at the start of its progression, when the elimination of the problem is simple and not costly. The knock in the engine can be caused not only by its detonation, but also by other problems not related to this precedent. If the causes of detonation of the injector engine can be identified through a special sensor installed on the car from the factory, then the timely fixation of the problem on carburetor models of cars depends directly on the attention of the owner and his ability to “hear” the car. Let’s consider in more details the most popular reasons of incorrect combustion of the fuel mixture, the knowledge of which will help to prevent many problems with functionality of the car and its concrete working units.

Underestimated octane rating of the fuel

Often the car owner wants to save some money on car maintenance, so he or she engages in the method of filling the car at the points of dubious origin. This method of saving allows refueling with inexpensive fuel, the quality of which does not meet the standards of international class. As a result, the consumer pours into the car a depleted mixture or liquid with a reduced octane rating, which directly determines the functionality of the engine, provoking detonation of the engine and not only. In the vehicle data sheet the manufacturer indicates the technological characteristics of the fuel that should be used when operating the machine. Filling a car with a mixture with an octane number several orders of magnitude lower than recommended by the manufacturer, provokes the rise in operating temperature of the unit under load, as well as increasing the pressure in the ICE. The cause of malfunction in this situation is premature ignition, which provokes a longer combustion of fuel. This process occurs due to under-compression of the cylinders, and provokes the subsequent detonation factor, which consists in the formation of carbon deposits on the surfaces of the internal combustion engine elements.

Fouling on the inner surfaces of the cylinder

Accumulations on the internal surfaces of internal combustion engine components are mainly caused by prolonged use of low-quality fuel and a lack of systematic maintenance of the engine in accordance with regulations. Deposits in the form of carbon deposits on the cylinder walls lead to a decrease in the cylinder working volume, which provokes, respectively, an increase in the compression of the fuel mixture, followed by its uncontrolled combustion. As a result, the prospects of detonation in the engine increase significantly.

Incorrectly selected spark plugs

The purchase of inexpensive spark plugs that do not meet the criteria specified by the manufacturer can be the cause of unauthorized ignition of the fuel mixture in the combustion engine. The purpose of the spark plugs is to act as the ignition timing controller of the fuel in the combustion chamber. Defective or inadequate spark plugs can reduce the cylinder displacement, which in turn increases the compression of the mixture and the engine temperature. All these phenomena in a complex combination provoke incorrect ignition of the fuel mixture and detonation processes. When in predominant manifestations there is engine detonation after switching off the ignition, the driver should check the spark plugs for performance, replace them if they do not meet the parameters specified in the regulations of the operation of the machine.

Options for troubleshooting

If there is a problem in the functioning of the engine, it should be corrected as soon as possible to avoid more serious disruption of the unit. If there is a problem, then there are options for its elimination. Let’s try to figure out how to eliminate engine detonation and whether it can be done without necessarily turning to professionals at the service station. The simplest solutions to the question of how to remove engine detonation, derive directly from the main root causes that provoke its appearance. To begin with, it is worth comparing the facts, when the unpleasant symptomatology from the side of the engine operation appeared. If detonation began immediately after the next refueling of the car, most likely, the reason lies in the quality of the fuel. In such situation it is better to drain completely low-quality liquid, refuel only at certified filling stations, buying fuel which is recommended to be used by a car manufacturer. The second useful advice to car owners, faced with the problem of detonation of the engine, is to check the spark plugs, if necessary – their replacement.

Owners of carburetor cars with detonation should check the ignition angle, the wrong position of which can provoke the appearance of the problem. In injector systems, such a malfunction is solved by the control unit, receiving data from the detonation sensor in automatic mode. When the system cannot automatically deal with the problem, an alarm warning appears on the dashboard of the machine, which requires qualified intervention. When removing detonation by manipulating the ignition angle, make sure that unauthorized intervention does not cause accelerated wear on the engine. Remember, not to look for methods to solve the problem of how to eliminate engine detonation, it is important to carry out effective preventive procedures that prevent the occurrence of malfunctions in the unit. Detonation prevention consists of the following activities:

1. Conducting regular maintenance of the cooling system of the machine, which will prevent overheating of the engine, and, accordingly, will be a reliable prevention of detonation.
2. Timely maintenance of the engine with mandatory oil change according to the regulations.
3. In order to avoid the formation of carbon deposits in the engine, subject it to periodic loads, which increase the efficiency of heat removal from the unit.
4. When carrying out engine repairs and replacing replacement system components, buy only parts that meet the requirements set out in the car’s data sheet, giving preference to purchases from certified outlets.

To summarize

Engine detonation is a problem with which the owner of any make and model of car may encounter. There are many reasons for this unpleasant phenomenon, but they all lie in the use of unapproved equipment, poor-quality parts or consumables in the car maintenance process, as well as inattention to the functionality of the motor. Detonation is a prospectively dangerous phenomenon that is fraught with costly powertrain repairs. Be attentive to the engine of the car, react immediately to unpleasant changes of its work – it will help to provide the engine a long service life and a trouble-free way of life.