Why do you need spark plugs in a diesel engine? Glow plug. How to check a glow plug in a diesel engine

Allows you to raise the temperature in the cylinders before starting the power unit. In other words, due to the incandescent elements, the combustion chamber is preheated after turning the ignition key, as well as further maintaining the temperature until a certain warm-up of the engine. This is necessary due to the peculiarities of ignition of the fuel-air mixture in a diesel engine. In such engines, the mixture of air and diesel fuel ignites independently, and not from an external source (spark plug spark in gasoline analogues). Diesel fuel burns from heat due to strong compression.

We also recommend reading the article about. From this article you will learn about the features and criteria for selecting a battery for engines of this type, as well as why there are special requirements for a diesel battery compared to the selection of a battery for gasoline analogues.

For this reason, the ease of starting a diesel engine depends on the serviceability of the parts responsible for heating. Let us add that malfunction of glow plugs most often manifests itself at subzero temperatures. Next, we will look at simple and affordable methods that allow you to quickly check the glow plugs on a diesel engine with your own hands and determine the cause of difficulty starting a diesel engine.

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Self-check of diesel engine glow plugs

As already mentioned, glow plugs ensure reliable starting of a diesel engine, which is especially necessary in cold weather. Conventionally, such a solution can be considered a kind of heater. On different models of diesel cars, such solutions may differ in the operating algorithm and general implementation scheme. One thing they have in common is the presence of a glow plug screwed into the block.

Early developments involve constant switching on of the glow plugs on a diesel engine in parallel with the ignition being turned on, that is, every time you try to start a diesel engine, the glow plugs heat up regardless of the current temperature. As for more “fresh” diesel engines, the glow may not be activated by the system if the engine is already warmed up or the ambient temperature is positive.

These features must be taken into account separately before checking the glow plugs. It will be necessary to separately find out under what conditions the elements for heating the combustion chamber are used on a specific diesel engine model. The inclusion of glow plugs is accompanied by the lighting of a separate indicator lamp, which displays a spiral pictogram on the dashboard inside the car. At the end of this solution for warming up the chamber on a diesel engine, the indicated light goes out.

It should be added that in the event of a malfunction of one or even a pair of glow plugs, the engine can start normally provided the temperatures outside are above zero. In other words, the warrior simply does not notice the malfunction. In winter, the situation changes, since starting a diesel engine with faulty glow plugs in cold weather becomes very difficult or even impossible.

In such situations, when the diesel engine does not start, the first thing you need to do is check the quality of the heating and combustion gauges. Glow plugs can be checked in the following ways:

connect glow plugs directly to the battery ();
evaluate the quality of spark formation on glow plugs;
check the glow plugs with a multimeter tester;

Checking glow plugs directly from the battery

To check the glow plugs by connecting them to the battery, they should be unscrewed from the engine. Note that for accurate diagnostics it becomes necessary to unscrew all installed elements. Also, in some cases, it will be necessary to dismantle certain components on the engine itself that do not allow easy access to the spark plugs. These nuances are a significant drawback of this verification method. Additionally, you will need a special tool, certain skills and free time.

Remember, you need to be very careful when unscrewing and tightening the glow plugs, as there is a risk of breaking off the glow plug. If the glow plug has broken off, then more serious repairs will be required to remove the remainder from the diesel engine block head.

The advantages of testing from a battery include the accuracy that this method provides. The condition and performance of the heating element are assessed separately and visually. This eliminates the possibility of installing parts that work but do not provide the proper degree of incandescence.

To diagnose the glow plug from the battery, you should take a wire with insulation about 50-60 cm long. Then the glow plug removed from the engine must be turned over so that the part on which heating occurs looks up. Afterwards, the glow plug is powered by the central electrode on the “plus” of the battery. Next, a piece of pre-prepared negative wire connects the battery to the side of the spark plug housing. The next step is to check the heating rate and its efficiency. Fast and full heating of the heating element is a sign of performance. Slow heating and/or partial heating of only the tip indicates the need for replacement.

Diagnosis of a glow plug based on the intensity of spark formation

Another way to check glow plugs on a diesel engine is to evaluate the intensity of spark formation after power is supplied from the battery. For such a test, an insulated wire is required (similar to the feather method). Then at the ends it is necessary to remove the insulator so as to expose 100-150 mm. wires.

Next, the power wires are removed from the glow plugs, after which the wire, stripped at the ends, is attached with one side to the positive terminal of the battery for testing. The other end must be passed over the central electrode of the element being tested to heat it up. Next you should pay attention to the following signs:

if the part is faulty, then there will be no sparking;
partial performance and low heat appear in the form of a weak spark;
on a fully operational element, the spark is strong, the sparking process is quite intense;

Checking the resistance of glow plugs with a multimeter tester

You can also check the glow plugs with a multimeter. This method requires less time and is the simplest. For diagnostics, you do not need to unscrew the glow plugs from the head. It is enough to disconnect the power wire from the central electrode of the spark plug being tested. Let us add that, structurally, the glow elements on a diesel engine can either have separate wires for each spark plug or be connected by one circuit.

It should also be noted that it will not be possible to simultaneously check the heating efficiency with a tester, which is considered a definite disadvantage. The fact is that a multimeter can show the serviceability of the element, but the combustion chamber will still be poorly heated.

To check glow plugs with a multimeter, switch the device to the “ohmmeter” operating mode. This is necessary to measure the resistance of the filament elements. To do this, the “+” tester probe is applied to the central electrode of the spark plug, and the negative terminal touches the side of the housing. The absence of readings on the device will indicate that the glow plug is faulty and requires replacement.

Before the onset of the cold season, the glow elements should be checked regardless of whether they are good or not.
Checking on a diesel engine by assessing the spark is recommended only for older cars. You should not test glow solutions using this method on a “fresh” model, which is equipped with a complex
If a malfunction is detected, it is optimal to replace the entire set, rather than one or two failed elements.
Try to purchase products from well-known manufacturers, since cheap solutions have a noticeably shorter service life and often demonstrate low efficiency of the heating element.

Finally, we would like to add that in order to reliably start a diesel engine in winter, it is necessary to select the right diesel fuel, fill it with high-quality diesel fuel according to the season, and, if necessary, use it. Also, in the case of diesel engines, it is advisable to install a diesel fuel pre-heater or.

Why are glow plugs needed for diesel engines?

In diesel power units, the fuel-air mixture is ignited not by a spark, but by compression. In this case, an external ignition source - a spark - is not needed; in a mixture of air and diesel, ignition occurs independently. Thanks to the work of the spark plugs, after turning the ignition key, the combustion chamber is preheated.

The performance of glow plugs is directly related to the starting speed of a diesel engine. Serviceable spark plugs ensure stable engine operation and quick starting.

Glow plugs for diesel - types

Glow plugs produced today for cars with a diesel engine can be divided into two groups - open and closed.

Open glow plugs - they are also called rod or pin. During operation, fuel enters the heated part. They are less durable and more susceptible to various contaminations. During operation, these candles can oxidize and become unusable. To extend their service life, the cuff rod should be secured as tightly as possible.
Closed glow plugs - consist of a spiral and a shell, the internal space is filled with ceramic powder. Spare parts are characterized by durability and a high degree of strength; parts rarely suffer mechanical damage and operate stably for a long time. These candles do not oxidize.

Properties of diesel glow plugs

The spark plugs heat the fuel-air mixture in the injection zone in seconds. The heating temperature ranges from 850-1000°C. At the same time, glow plugs for a diesel engine continue to operate even after the power unit is started, until the coolant is warmed up to the required temperature (at least 75°C).

Working principle of glow plugs

Glow plugs are installed in each combustion chamber. After starting the car, electricity is supplied to a spiral resistor, which heats up to a temperature of 100°C. This leads to self-ignition of the fuel. That is, in essence, glow plugs are needed to warm up a diesel engine, but they do not create a spark.

In cars with a diesel engine, there is always a glow plug sensor, which informs the owner if parts fail.

In older car models, the glow plugs are turned on every time the engine is started. Modern cars use diesel glow plugs only at low temperatures (from +5°C and below). To determine malfunctions of glow plugs in diesel cars, a special indicator installed on the instrument panel is used.

Owners of diesel cars will find it very useful to know how to check glow plugs, since they are an integral part of a diesel engine, and any malfunction in their operation will create discomfort or even force them to switch to public transport.

Replacing glow plugs - is it so important to do it on time?

The main function of these parts is to start the engine, because, as you know, its operating principle is somewhat different from gasoline, since the fuel in this case is ignited not by a spark, but by compression. And high temperature promotes more efficient ignition, which is what glow plugs provide. Modern cars are equipped with types that heat the fuel not only before starting, but also for several minutes afterwards, thanks to which the engine’s idle speed becomes more stable, and the emission of harmful substances reaches a minimum due to more efficient fuel combustion.

Undoubtedly, in the warm season there is practically no need for them, but as soon as the ambient temperature reaches +5 °C, it becomes almost impossible to start a car without this element. Therefore, it is very important to monitor their condition, especially with the onset of cold weather, and for this you need to know how to check the glow plug. But first, let’s take a closer look at their connection diagram in order to understand at what point you need to sound the alarm.

Glow plug connection diagram and signs of malfunction

In principle, they can be compared to an electric heater. The spark plug rod is located in the pre-chamber in such a way that its tip is located directly on the border of the vortex of the working mixture created by the nozzle. The glow plug connection circuit provides automatic supply of electric current immediately after turning the ignition key to the operating position. They heat up themselves to a very high temperature and, accordingly, warm up the combustion chamber, as well as the air entering it.

The glow plug control unit is responsible for their proper functioning. The algorithm for its operation is as follows: after turning the key, the spark plugs are connected directly to the battery, at the same time the corresponding light on the instrument panel lights up, after some preheating time this light goes out, which indicates that the engine is completely ready to start.

The first sign that there is a failure in the electric heating system is a non-working indicator. This may indicate a failed fuse or temperature sensor. If the indicator burns for a long time, it indicates the need to replace the thermal switch, and if this is ignored, the thermal pin may burn out, and then the incandescent will be needed. True, the indicator sometimes may not signal a possible breakdown.

Also, a clear sign that a spark plug is starting to get “naughty” is trouble starting the engine. And in this case, checking the glow plugs is urgently necessary.

How to check glow plugs yourself?

You can do the diagnostics either at a service station or on your own; for this you only need a clamp-on ammeter. You must proceed as follows. The first to be disconnected is the supply drive going to the positive contact of a particular spark plug; this drive must be connected to the “plus” of the ammeter. The second pole of the ammeter is connected to the positive contact of the spark plugs themselves. The system turns on and the current strength is determined. Since each participant in the motor operation consumes approximately 12 A, therefore the total should be 48 A; if this value is less, then there is a malfunction.

There is another way to check the glow plugs in an inverted state. The removed spark plugs should be installed on a common bus, ends up, and each of them is connected to ground using wires of a large cross-section of the housing. Then, their condition is visually determined (a spark that appears will indicate a malfunction). Using a multimeter or other specialized instruments, you can check the resistance of the glow plugs; it should be less than 5 ohms, but if its value approaches infinity, then the heating coil is faulty.

Spark plugs in a diesel engine ensure guaranteed starting of the power unit when cold. The principle of their operation is to bring fuel under high pressure to the required temperature using a special relay. A diesel engine has as many spark plugs as there are cylinders in it. There is one spark plug for each engine cylinder.

The principle of switching on a diesel engine

The fuel-air mixture, which is under pressure in the cylinder, is heated to 900°C. To ensure fire conditions, the structure is highly durable. The combustible mixture is ignited by the compression ratio, and not by the spark plug. At ambient temperatures below plus 5°C, down to severe frosts, the combustion chamber requires forced heating using ceramic or pin glow plugs.

The glow plug in a diesel engine is capable of heating the injection zone to 1000°C in a matter of seconds. When the diesel engine is turned on, these devices operate until the coolant temperature reaches plus 75°C.

Due to the increased demands of environmentalists, thanks to their unique properties, spark plugs begin to function at idle speed. The design of these parts helps reduce the amount of harmful emissions from a diesel engine into the atmosphere.

Design features of various types of candles

These structures can be made of either closed ceramics or open metal. The heating element is made in the form of a spiral.

Metal pin structures have spirals: heating and adjustment. Thanks to the first, rapid heating occurs, the second serves to protect the structure from overheating.

The composition of ceramic parts is more complex:

Metal body.
Heating tube.
Connecting bolt and nut.
Adjustment spiral.
Ceramic filling.
Central electrode.
Threaded part.

Ceramic parts are preferred due to their ability to produce heat quickly and provide very high temperatures.

Under the influence of electric current, the coil heats up. The high temperature in the motor prevents the element from heating above 850°C; heating lasts for a short time: from 4 seconds to 2 minutes. The duration of heating is monitored by an electronic control unit, which monitors the temperature of the coolant through special sensors.

While heating continues, the control light located on the instrument panel lights up. Turning off the lamp indicates that the engine is completely ready to start.

The glow plugs continue to work after the engine is turned on, continuing to warm up and ensuring the most complete combustion of the air-fuel mixture, reducing harmful emissions.

Methods for checking spark plugs

You can check the voltage in the elements using a multimeter or car battery.

In order not to dismantle the device, just connect it to the battery. The connection diagram is as follows: the minus is connected to the spark plug body, and the plus to the terminal, respectively. In a working unit, the coil heats up within a few seconds. The absence of heat indicates the need to replace the device.

When checking the spark plugs in the injectors, you need to unscrew the elements and examine the glow of the pins, which should glow. A difference in the glow intensity of at least one element indicates the need for additional verification by measuring its resistance. In order to avoid rapid failure of the remaining elements, the entire set is replaced at once, regardless of how many parts turned out to be defective.

It rarely happens that more than two devices fail, in which case it is necessary to check the electrical wiring or electronic control unit.

Using a multimeter, the performance of a dismantled spark plug is determined by the “diagnosis” method.

In modern cars, these components can be checked through self-diagnosis, additionally using an indicator located on the instrument panel, which gives a signal when a spark plug breaks.

Description of signs of malfunctions of incandescent elements

Failures of glow plugs are manifested by the following defects:

The engine does not want to start.
Uneven operation of a cold engine.
The appearance of white exhaust gases.

If the car owner has recently replaced all the spark plugs, then the reason may lie in a malfunction of the element due to the fault of the manufacturer. The defective part must be unscrewed and replaced with a new copy. Malfunctions of incandescent elements are most noticeable in winter. A decrease in ambient temperature causes more signs of faulty filament elements to appear.

To facilitate the dismantling process, a special diesel engine glow plug puller is used. It must be used in conjunction with a tool adapted for a square or hexagonal head.

Why do spark plugs fail?

The service life of modern diesel glow plugs is 60 thousand kilometers, subject to operating conditions. If damage to the shell of the spiral occurs, the entire device will fail earlier, because dirt and moisture penetrate into the resulting crack, and the spiral closes to the housing. The shell may fail for the following reasons:

failure to observe thoroughness and accuracy when installing the glow element into the motor;
the appearance of electrochemical corrosion over a long period of time;
installation of spark plugs that do not correspond to the models of this type of diesel engine.

These devices are very important - they ensure both uninterrupted starting of a diesel engine at sub-zero ambient temperatures and significantly reduce the amount of exhaust harmful gases.

One of the significant differences between diesel and gasoline engines is the difficult starting conditions at low temperatures due to the principle of its operation. Glow plugs should ensure a confident start of the engine, but if they fail, the driver will face serious problems.

Purpose and design

The fuel-air mixture in the cylinders of a diesel engine ignites at a temperature of 800-850 degrees. But in a cold diesel engine (less than 50-60 degrees), such a temperature cannot be achieved by air compression by pistons alone. That is why glow plugs were introduced into the design of this type of engine, the working part of which is located in the combustion chamber to heat the air.

The main task of the glow plug is to reach operating temperature as quickly as possible after turning the ignition key to the first position in order to heat the air in the combustion chamber. The plugs heat up to 850-1300 degrees within 2-30 seconds and on average consume a current of 8-16 amperes (i.e. 96-192 W) each. The duration of current supply to the spark plug and the voltage level are controlled by a relay or a special electronic unit. Having “turned off” the light on the dashboard, which prohibits the driver from turning on the starter, the relay continues to heat the spark plugs for some time - up to 3 minutes - with the engine running. However, some modern spark plugs are disconnected from the network immediately after the starter is turned off, since they remain hot for the time required to warm up the engine. In the most advanced designs, the electronics monitor the engine temperature, and if it recognizes it as warm enough, it does not turn on the spark plugs at all.

A glow plug is a heating element mounted in a housing and covered with a casing. In the simplest case, it is a spiral of refractory metal. More complex candles have two spirals made of different materials. By changing their resistance depending on the degree of heating, they provide automatic temperature maintenance and avoid overheating without the help of an external relay.

Symptoms of the problem

In a modern diesel engine, a working spark plug with a normally functioning control unit warms up to operating temperature in a few seconds.

Lack of heating of the internal volume of the cylinders is the most likely reason for difficulty starting a diesel engine. A working engine should start immediately after turning on the starter, from the first revolutions of the crankshaft. In warm weather, the failure of one spark plug is not always noticeable at start-up, but in the first minutes after start-up, some engines (depending on the model and condition) will run unevenly, since the combustion process in a cold cylinder is disrupted. Two problem spark plugs already seriously complicate starting. Failure of three or four spark plugs at once is unlikely, so if the engine does not start, the reason may lie in the control relay or wiring. There are cars in which a lamp on the dashboard indicates a faulty spark plug.

With faulty spark plugs, a warm (60 degrees and above) diesel starts without problems.

Causes of problems

The nozzle should not “pour” diesel fuel in one stream directly onto the spark plug.

The spark plug fails for two reasons: the life of the spiral is exhausted (approximately after 50-75 thousand kilometers), or the fuel equipment is faulty. If one spark plug fails on an old car, the others also need to be changed - they will soon fail anyway.

The life of a spark plug is shortened by faulty fuel equipment, for example, a dirty or worn nozzle that directs a powerful jet of fuel directly to the working element of the heater. This causes a hole to form in the heater shell, and the spiral is destroyed. Finally, the spark plug is easy to break if installed improperly. The long spark plugs of many modern engines break during dismantling because they stick to the cylinder head.

A faulty control relay can cause the spark plugs to overheat - their shell is deformed, melts, and the spiral burns out. The relay itself can also “burn out”, and the wires coming from it can break or fray due to improper installation after repair.

Diagnostics

An extinguished warning light will indicate that the spark plug is warmed up and you can turn on the starter.

The simplest diagnosis of glow plugs is to check their electrical conductivity. The spiral must conduct current, its resistance in a cold state is in the range of 0.6-4.0 Ohms. If you have access to the candles, you can “ring” them yourself: not every household tester is able to measure such a low resistance, but any device will show the presence of a heater break (the resistance is infinity).

More accurate diagnostics, tracking the characteristics of each spiral, are carried out by specialists. If you have a non-contact (induction) ammeter, you can do without removing the spark plug from the engine. But it is often necessary to check the unit on a special stand and visually inspect the working part, which may show signs of overheating - melting, deformation of the tip, even to the point of its destruction.

In some cases - including if all spark plugs fail at once - it may be necessary to check the vehicle's electrical equipment. Namely, the spark plug control relay and its circuits.

Igor Shirokun
Photo Bosch, Beru

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