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.
In our article we will look at what glow plugs diesel requires, the operating principle of this element and its varieties. This is not at all the spark that is usually meant when talking about a gasoline engine, so it’s time to clarify.
Glow plugs: diesel and gasoline - what's the difference?
So, as you know, a diesel engine differs from its carburetor prototype. Indeed, in the second case, spontaneous combustion occurs. When fuel is added, the intake air, compressing, heats up to 700-900 °C, which is what leads to spontaneous combustion. Due to the fact that a diesel engine is designed differently than a gasoline engine, the principles of their operation are also different. In a gasoline engine, combustion occurs from a spark, but in a diesel engine, from compression.. In order for the fuel to ignite, it must be heated.
In the summer, this will not be difficult, since it is quite warm, but in frosty conditions and in the case of a cold start, additional heating must be provided in the combustion chamber. A screw is screwed into each chamber. At the moment when electrical energy passes through the spiral resistor, heating it to a temperature of 100 ° C, fire occurs. Thus, we can say that the glow plug in the diesel engine caused the diesel fuel to self-ignite.
Spark plugs in a diesel engine do not serve as a source of spark to ignite the combustible mixture; they are only needed to heat it up.
How is the glow plug checked in a diesel engine?
There are several ways to check the working condition of the elements. This can be done through the engine or separately from it. In order to check the performance of glow plugs outside the engine, that is, without screwing them in, you need an ohmmeter or voltmeter. These devices are used to check the voltage status. If one or the other is missing, you can check in the following way: connect the spark plug to the battery, connect the plus to the terminal, and connect the minus to the body of the element being measured.
After a few seconds, the spiral of a working spark plug will heat up, then it will begin to glow, this will indicate its functionality. If no reaction occurs, it is necessary. Another way to check their performance is to use a tire. To do this, install inverted candles on it, the ends of which should be directed upward. Then, using wires with a relatively large cross-section, the “ground” is closed, attaching the conductors to the body of each spark plug.
Some engine repair instructions describe a method for checking the operation of glow elements through the holes intended for the injectors. Having previously unscrewed them, observe how the pins glow, red-hot from heating. If one or more elements light up less brightly than the others, or do not light up at all, you need to check their electrical connections and then check the resistance value. 
What kind of glow plugs can a diesel engine have?
To always know the state of the glow plugs, diesel engines are equipped with an appropriate sensor. Such an indicator will indicate a malfunction; it lights up if there is a problem and goes out if the required heating temperature is reached. It is not always worth trusting these devices unquestioningly. Still, you need to protect yourself, and before the start of the winter season, you should check everything yourself. If at least one element in a diesel engine is faulty, it would be advisable to replace it.
Not everyone knows that these There are two types of incandescent elements - open and closed. Closed type candles, unlike representatives of the open type, are distinguished by high mechanical strength and durability in operation, since they do not oxidize. This type of device is based on a spiral, which is protected by a special shell filled with ceramic powder.
Open type candles are also called pin or rod candles. They are installed in the combustion chamber. In this case, a prerequisite is that the fuel gets on the hot part. Their performance depends on the absence of dirt and moisture on the surface. To prevent this, it is necessary to tightly fasten the rod of the cuff, which is made from silicone sealant or rubber. When you have chosen the required glow plugs for diesel, replacing them at a service station is preferable.
In appearance, glow plugs are similar to spark plugs in a gasoline engine, but they do not produce a spark. Used to start a diesel engine. They consist of a body, a tip and a heating element (metal or ceramic) - a spiral. The maximum tip temperature is 1350 degrees Celsius. The tip of a glow plug in a diesel engine consists of a pair of spirals - heating and regulating. The latter provides the spark plug with protection from overheating by increasing electrical resistance as the temperature rises. The heating coil provides heating of the combustible mixture and air.
There are two main types of glow plugs:
- pin - with a metal heating element, which is an alloy of iron, chromium and nickel. The inside of the case is filled with magnesium oxide;
- ceramic - the heating element is made of ceramic, which has increased resistance to temperature changes. The material for the manufacture of the protective shell is silicone nitrite.
Ceramic spark plugs heat up the fuel in just 2 seconds. Their use allows you to start a diesel engine without preheating.
Distinctive features include the resistance of the candle. It ranges from 0.5 to 1.8 ohms. Moreover, metal always has greater resistance than ceramics. Thus, while ceramics lose in resistance, they gain in the ability to use more powerful currents for heating.
Operating principle of the glow plug relay
The required amount of current is supplied from the glow plug relay, which ensures heating of the spiral and tip. The heat emitted by the tip enters the intake manifold and working cylinders of the engine, heating the working mixture to the required temperature.
When heated, it ignites as a result of compression under the influence of pressure forces from the working piston. But at the same time, overheating risks ignition of the working mixture even before it enters the cylinder, as a result of which the engine either refuses to work at all or its efficiency decreases. To ensure the desired heating mode, a glow plug relay is used.
It closes and opens the electrical circuit, providing the required amount of heating of the working mixture. After the circuit is closed, the current supplied to the spark plug heats the tip to the required temperature, after opening it “cools down”.
Checking the glow plugs yourself
This is often done by visual inspection. This allows you to identify malfunctions and irregularities in the operation of the fuel system, the condition of the piston group, and the correct operation of the electronic control system.
Defects on the spark plug
If the spark plug has not yet exhausted its working life, but upon visual inspection there are cracks and swelling in the middle of the body, then this indicates:
- increased voltage supplied to the spark plug. In order to clarify this fact, you need to measure the voltage supplied to the spark plugs by the on-board network using a multimeter;
- The glow plugs do not turn off for a long time. You can check this using an ohmmeter or by noting the response time of this diesel engine ignition element by clicks.
There is melting at the tip of the candle
It can form for the following reasons:
- premature fuel injection occurs;
- the nozzles are dirty, so the spray is not carried out correctly;
- overheating as a result of late ignition and weak compression;
- The pressure valve has failed. You can check by loosening the nut of the fuel line that goes to the injector. If this is so, then it will not be foam that will come out from under it, but fuel.
When examining the candle, pay attention to its thin part. It should not be melted, otherwise you need to prepare to replace it, even though it still works.
Where is the glow plug relay located and how to check and replace it?
Considering that this is an electronic device, it can be checked using a multimeter. But first you need to find the relay. Externally, it looks like a box that is attached to the car body. The place where it is fixed on the body is called the “mass”. It won't be difficult to find her. To do this, you just need to follow the wires that come out of the spark plugs.
When the location is established, you need to connect the multimeter by connecting the probes to the car body and the terminals that transmit current through the wires to the glow plugs and switch it to voltage measurement mode. The measurement is made with the ignition on. In this case, the output voltage should not be less than 12 volts. You can also measure the voltage at the battery terminals and compare it with what the multimeter shows at the relay terminals. If there is less on the relay, even by one volt, it is not working properly!
You can check the voltage between the relay terminals. In this case, it is necessary to take into account the standard resistance values.
There is another way to check the glow plugs on a diesel engine and the relay that regulates their operation. You need to smoke the candles, attach the wires to them and turn on the ignition. If they glow, then the spark plugs and relays are in good condition.
Replacing the relay is quite simple. To do this, you need to disconnect all the wires that go to it and remove the relay itself. Next, you will need to clean the junction of the relay with ground and install a new box.
Advice! When removing the plugs, it is advisable to remember their location or stock up on the relay circuit, otherwise you may assemble the device incorrectly.
It is best to select according to the car’s VIN code, because the type of electronic unit and engine system play an important role. After replacing the engine or tuning it, the selection is made using the following data: make, body type, year of manufacture, engine model.
When purchasing glow plugs, you must consider:
- their geometric dimensions;
- connection type;
- heating rate;
- the appearance of the candle itself, or rather its heating element.
Instructions for replacing glow plugs yourself
For this you will need:
- screwdriver;
- wrench;
- socket wrench;
- pliers;
- work gloves;
- some high temperature and graphite lubricants.
If there is protection for the motor housing, it must be removed. Field then disconnect the connecting terminals. Next, very carefully unscrew the spark plugs themselves. After stripping the contacts and cleaning the threads, new glow plugs are installed. In this case, it is better to completely replace them, regardless of the condition of any individual spark plug.
Having an understanding of what glow plugs are for, what they are made of, how they work and how they are replaced, any car enthusiast will be “armed” with the necessary information and will be able to restore normal engine performance if these ignition elements are the cause.
If you have any questions, leave them in the comments below the article. We or our visitors will be happy to answer them
The operating principle of glow plugs on diesel engines differs from spark plugs on gasoline engines. At the same time, the cold start of the power unit at low temperatures outside the car depends on their timely replacement and correct installation. This article describes the design features of these products, as well as methods for diagnosing them.
Placement of CH inside the engine.
Unlike power units running on gasoline, diesel engines do not have a spark plug; they are equipped with glow plugs (abbreviated as CH). They serve as a heating element, the main function of which is to heat the combustion chamber to simplify cold starting of the engine. Ignition of the fuel-air mixture in diesel engines occurs due to the formation of high pressure inside the combustion chamber at the end of the compression stroke, when the piston reaches top dead center. Ignition of the fuel mixture is possible only when the fuel is heated. In summer, the temperature outside the car is sufficient, heating is not needed, but in winter, if the air temperature is less than +5 0 C, it is necessary to warm up the combustion chamber. For this purpose, MVs are installed for each chamber. The rod of the product is located in the pre-chamber, its end reaches the boundary of the vortex of the working fluid created by the nozzle. Electric current is supplied to the spark plug coil automatically when the ignition key is turned. The products are heated to the required temperature and thus warm up the chamber and the air entering it.
Please note that there are types of diesel engines that do not have CH. In most cases, these are auto engines driving industrial equipment or low-speed tractor engines. In such cases, a special heating grill is used, built into the intake manifold; it replaces the CH.
The car has a special CV control unit. When you turn the ignition key to the operating position, the spark plugs are connected to the battery, and an indicator lights up on the dashboard, which goes out when the engine is fully warmed up, indicating that the car is ready to start.
Varieties
Design features of a ceramic rod There are the following types of candle products:
- closed type, in which the spiral can be open or placed inside a protective casing;
- open type.
In the first version, the heating element is placed in a candle body filled with a special powder that conducts heat. They separate products with a spiral made of metal or ceramic.
The main advantage of ceramic products is the achievement of maximum heating temperature in a very short period. This ensures better engine starting without warming up, reduces the amount of toxic exhaust gases, and increases the service life of spark plug elements and the engine. The service life of the candle is increased because the heating element placed in the casing does not oxidize, plus it is protected from mechanical influences.
Open-type glow products are located in the combustion chamber; for their effective operation, the fuel mixture must flow onto the hot part of the rod.
According to the time it takes to reach operating temperature, the glow plugs are divided as follows:
- conventional, the product warms up in less than 1 minute;
- fast-acting, the desired temperature is reached within 10 seconds;
- self-regulating, they warm up in 5 seconds.
In the latter option, the heating speed is achieved due to the presence of two spark plug spirals. Such products are very effective in operation and have a long service life, which allows them to displace the first two types of candles from the shelves of the car market.
Diagnosis at home
One of the variations of the CH design. - Plug
- Printed circuit board with electronics
- Glow plug housing
- Heating rod
- High voltage connection
- Measuring diaphragm
- Padding
There are several ways to check the need to replace glow plugs on a diesel engine:
- Using battery. To carry out diagnostics, follow the sequence:
- take an insulated wire 50 cm long;
- turn the spark plug over so that the heating element is at the top and install its central electrode on the “+” terminal of the battery;
- connect the “-” terminal of the battery to the spark plug body using an electrical wire;
- the serviceability of the candle can be judged by the degree of its heating; if the heating element quickly warms up by at least 50%, then the product is working properly; in situations where only the tip of the heating element is heated, it is worth replacing the candle.
Among the disadvantages of this method, one can highlight the need to unscrew each spark plug device, and it may be necessary to dismantle some elements of the car that prevent access to the spark plug.
- Using a multimeter. Using this method you do not need to remove the candles. To carry out diagnostics, perform the following manipulations:
- disconnect the current conductor of the central electrode from the glow products;
- connect the positive probe of the multimeter to the central spark plug electrode, touch the side of the case with the minus probe;
- set the device to the ohmmeter position;
- If there are no readings on the device display, we can talk about a breakdown of the heating element - the spark plug requires replacement.
The disadvantage of this method is the diagnosis of products with low heat. During testing, the device will indicate that there is no breakdown, and heating of the combustion chamber will be insufficient.
- Using insulated wire. The verification scheme is as follows:
- remove the insulating layer, about 2 cm from each side of the wire (the length of which is up to 1 m);
- disconnect the spark plugs from the supply wire and tire;
- attach one end of the insulating wire to the “+” terminal of the battery, and touch the central contact of the spark plug with the other.
- a spark appears on a working spark plug; if the product is weakly heated, then the spark is insignificant.
No spark indicates a completely faulty spark plug. The disadvantage of this method is the possibility of checking spark plugs on old-style cars, “without brains”.
Conclusion
How many glow plugs on a diesel engine depends on the design features of the car. There are engines running on diesel engines, equipped with direct injection; they do not have pre-chambers and CH.
Installing the CH on a diesel engine allows you to improve engine starting after a long period of inactivity or at low temperatures outside the vehicle. These products make it possible to improve the conditions for the formation of the working mixture. Modern CVs can continue to operate for a short time after starting the car engine, thus reducing the amount of harmful substances in the exhaust gases, and also stabilizing the combustion process. During steady engine operation, they perform an additional function - they improve fuel atomization. The fuel stream breaks up when it hits the spark plug tip, this improves the occurrence of turbulence in the combustion chamber.
The task of glow plugs is to heat the air in the combustion chamber of a diesel car as quickly as possible, since ignition of the mixture, in this case, occurs at a temperature of 800–850 C and this indicator cannot be achieved by compression alone. Therefore, after starting the engine, spark plugs should work until until its temperature reaches 75°C.
In relatively warm weather, the failure of one or two glow plugs may be unnoticeable, but with the onset of cold weather, difficulties immediately arise in starting a diesel engine and the need to check the spark plugs.
Glow plugs
The duration of the current supply to the spark plug and the voltage level are controlled by a relay or a special electronic unit (candles, when heated to 1300 degrees for 2–30 seconds, consume a current of 8 to 40A each). The dashboard shows the driver that it is too early to turn the starter until it goes out. In modern designs, electronics monitor the engine temperature, and if the engine is warm enough, it does not turn on the spark plugs at all.
With faulty spark plugs, a warm (over 60 °C) diesel engine starts without problems; starting a diesel engine is difficult only when cold.
A glow plug can fail for two reasons:
- the spiral resource has been exhausted(approximately after 75–100 thousand kilometers);
- fuel equipment is faulty.
Signs of faulty glow plugs
Indirect signs presence of malfunction:
- When starting from the exhaust white-gray smoke is coming out. This indicates that fuel is flowing but is not igniting.
- Rough operation of a cold engine at idle. The noisy and harsh operation of the engine can be noticed by the shaking plastic parts of the interior due to the fact that the mixture in one cylinder ignites late due to the lack of heating.
- . You have to do several repetitions of spinning the engine with the starter.
Clear signs an unusable glow plug will be:
- Partial tip destruction.
- Thick carbon layer on the tip near the building.
- Swelling of the glow tube(occurs due to excess voltage supply).
How can you check the glow plugs of a diesel engine?
How to check?
Depending on the model and age of the car, there are different principles of operation of the diesel engine heating system:
- In older cars, glow plugs usually turn on almost every time the engine is started.
- Modern cars can start successfully even without glow plugs at above-zero temperatures.
Therefore, before starting to diagnose the diesel preheating system, you need to find out at what temperature conditions the combustion chamber is heated. And also, what type of candle, since they are divided into two groups: rod (the heating element is made of a refractory metal spiral) and ceramic (the heater is ceramic powder).
Environmental standards Euro 5 and Euro 6 provide for the operation of diesel engines with ceramic spark plugs, since they have the function of pre-starting and after starting heating, which allows the fuel to be burned in a cold engine, as well as an intermediate glow mode necessary to ensure regeneration of the particulate filter.
To check diesel spark plugs Ford, Volkswagen, Mercedes or other car, can be used in several ways, and, depending on whether they are unscrewed or on the engine, the principle will be the same. Functionality testing can be done using:
3 ways to check glow plugs - video
- Battery. On the speed and quality of incandescence;
- Tester. By checking the break of the heating winding or its resistance;
- Light bulbs(12V). The simplest test for breakage of the heating element;
- Sparking(can only be used in old diesel engines, since new ones are dangerous due to ECU failure);
- Visual inspection.
The simplest diagnosis of glow plugs is to check their electrical conductivity. The spiral must conduct current, it cold resistance within 0.6–4.0 Ohm. 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).
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 inspect the working part, on which signs of overheating may be noticeable - melting, deformation of the tip, up to its destruction.
In some cases, in particular 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.
We will describe all the ways to check diesel glow plugs. The choice of each of them depends on skills, availability of equipment, tools and free time. But ideally, you need to apply everything together, plus a visual inspection.
How to check glow plugs without unscrewing them (on an engine)
Checking glow plugs should begin by finding out whether voltage is supplied to them at all, since sometimes the contact of the supply wire simply oxidizes or weakens. Therefore, checking without tester(with ohmmeter and voltmeter modes) or as a last resort 12 volt light bulb, no way to carry it out.
Glow plugs on the engine can be checked except that on their overall performance, since the intensity and speed of heating of the heating element cannot be seen (only on some engines you can unscrew the injectors and look through their wells). Therefore, the most reliable diagnostic option would be to unscrew the spark plugs, check the battery and measure the indicators with a multimeter, but for a quick check, at least something will do.
The principle of checking a glow plug with a light bulb
So, the first way to check the glow plug on the engine (or already unscrewed) - use of controls. Two wires are soldered to the 21 W lamp (a light bulb of size or stops will do), and with one of them we touch the terminal terminals of the spark plugs (having previously disconnected the supply wire), and with the second to the positive terminal of the battery. If the light comes on, it means there is no break in the heating element. And so on for each candle in turn. When the light bulb glows dimly or doesn't burn at all - the candle is bad. Since the method of checking a glow plug with a light bulb is not always available, and its results are relative, the next step is checking with a tester.
Checking the spark plug
Checking the glow plug for a spark is similar to the previous method, only it is done without a light bulb and by intensively touching the threaded part.
Checking for sparking at the power cable connection point can only be produced on old diesel engines where there is no electronic control unit.
To check for spark you will need:
- A meter-long piece of wire, stripped of insulation at the ends.
- Disconnect the spark plugs from the power supply bus.
- Screw one end of the wire to the “+” of the battery, and apply the other, with tangential movements, to the central electrode.
- A strong spark will be observed on a serviceable spark plug, but a poorly heated spark will not form.
Due to the danger of using this method, it is not used on modern diesel cars, but know it, at least for how no need to check with a light bulb, Necessarily!
How to check glow plugs with a multimeter
Checking diesel spark plugs with a multitester can be carried out in three modes:
Checking the glow plug with a multimeter for a broken spiral
- in dialing mode;
- measure resistance;
- find out the current consumption.
Ring the break You can even test the heating element without unscrewing the spark plug from the engine, but to use the other two methods of checking glow plugs with a tester, it is advisable that they are still in front of you.
And so, for dialing mode you need:
- Move the regulator to the appropriate position.
- Disconnect the current supply wire from the central electrode.
- The positive probe of the multimeter is on the electrode, and touch the negative probe to the engine block.
- There is no sound signal or the arrow does not deviate (if the tester is analog) - a break.
Measuring glow plug resistance with a tester
This method will only help to identify a completely non-working glow plug, but you will not be able to identify problems with the heating element.
Much It's better to check the resistance with a tester, but for this need to know the nominal value, which a specific candle must correspond to. U good spark plug resistance spiral makes up 0.7-1.8 Ohm. Since quite often the spark plugs, although they still fire, already have a high resistance, as a result of which they consume less current and the control unit, having received the corresponding signal, thinks that they have already warmed up and turns them off.
With a high degree of reliability of the result regarding the suitability of the spark plug, and without unscrewing it from the diesel engine, you can find out checking current consumption.
To measure, you need to: on a cold engine, disconnect the supply wire from the spark plug and connect one terminal of the ammeter to it (or the plus on the battery), and the second to the central terminal of the spark plug. Turn on the ignition and look at the current consumption indicators. Current consumption of a working spark plug incandescent, depending on type, should be 5-18A. By the way, note that in the first second of the test the readings will be maximum, and then, after about 3-4 seconds, they will gradually begin to fall until the current stabilizes. The arrow or numbers on the tester should decrease evenly, without jerking. All tested spark plugs from the engine must have the same current flow values. If something is different on some spark plug or nothing happens at all, then it makes sense to unscrew the spark plug and check the glow visually. When the spark plug is partially heated (for example, the very tip or the middle), the readings will differ significantly, and when there is a break, there is no current at all.
It is worth noting that with a single-pole power supply connection (when the ground is on the body), one pin plug consumes from 5 to 18 amperes, and a two-pole plug (there are two terminals from the glow plugs) up to 50A.
In this case, as when measuring resistance, it is desirable to know the nominal value of current consumption.
When there is no time to make a test light or tools for removing spark plugs, or they are already lying on the table, checking with a multimeter may be useful. But it also has its drawbacks - this method, like checking with a light bulb, does not allow you to identify a candle with a weak glow. The tester will show that there is no breakdown, and the spark plug will not warm up the combustion chamber sufficiently. Therefore, to determine the speed, degree and correctness of heating, as well as in the absence of instruments at hand, it is imperative to check the spark plugs for heating with a battery.
Checking glow plugs using a battery
The most accurate and clear picture of the serviceability of the heating elements is given by checking the battery. Each candle is checked separately, and the degree and correctness of its glow is visible.
The principle of checking the glow plug with a battery
To check, you just need nothing - literally a piece of insulated wire and a working battery:
- We press the central electrode of the spark plug to the positive terminal.
- We connect the negative wire to the body of the heating element.
- Quick heating until red hot (and it should heat up from the tip) indicates serviceability.
- Slow heat or him absence at all – spark plug is faulty.
For a more accurate test, it would be a good idea to measure the speed at which the tip of the candle heats up to cherry red. Then compare the heating time of each candle relative to the others.
In a modern diesel engine, a working spark plug, with a normally functioning control unit, warms up to operating temperature in a few seconds.
Those candles that heat up earlier or later than the main group (the average time for modern candles is 2-5 seconds) are put aside for scrap. You may ask why throw away those that used to be, because it’s good? When the candles are of the same brand and the same type, heating ahead of time indicates that not the entire element is heated, but only a small part of it. At the same time, very often cracks in the body are observed in these places. So when testing for heating, it is advisable to know the characteristics of the spark plugs or take the values of a new one as a standard.
When the spark plugs, although they work, warm up to different temperatures and at different speeds, then, as a result, things happen (one is already igniting the fuel mixture, and the other is just burning after). Quite often, they can check all the spark plugs at once, connecting them not in series, as it would seem, but in parallel, then everyone will receive the same current strength.
When tested, all candles should heat up to a cherry hue within one second of each other.
The only difficulty with this method is that you will have to unscrew all the spark plugs, and this sometimes turns out to be quite difficult and time-consuming. But the plus is that in addition to checking for heating of the glow plugs, we also check for hidden defects.
A visual check allows you to identify not only defects, but also the operation of the fuel system, the operation of the electronic control, the condition of the piston, so always carefully inspect the glow plugs since they have already been removed.
There are defects on the spark plug
If the spark plugs have not yet reached the end of their service life, but already have signs of overheating (approximately in the middle of the heated rod), the body swells and cracks spread along the sides, then this is:
- Voltage too high. You need to measure the voltage in the on-board network with a multimeter.
- The glow plug relay does not turn off for a long time. Record the response time by clicks or check the relay with an ohmmeter.
Melting the tip of the candle
This may happen due to:
- Early injection of the fuel mixture.
- The nozzles are dirty, resulting in incorrect spraying. You can check the injection torch on a special stand.
- Weak compression and late ignition, and therefore overheating.
- The pressure valve has closed. Then the engine will work quite hard, and if you loosen (with the engine running) the nut of the fuel line leading to the injector, then not fuel, but foam will come out from under it.
When visually checking the thinnest part of the spark plug (the one that is located in the prechamber), make sure that it is darkened, but not with a melted iron body, and without cracks. Because even if it still works, it will not last long, and soon it will have to be checked again.
By the way, poor spark plug performance can occur due to insufficient contact with the supply bus. If the nut is loosely tightened due to vibration, it will loosen. But you shouldn’t pull too hard, as you can damage the electrode. Often candles are damaged by unprofessional actions when twisting/twisting. It is not uncommon that the wrong amount of torque can cause loss of compression, and their vibration will destroy the core in ceramic glow plugs.
Glow plugs- enough fragile, so it is advisable to unscrew them from the engine only if replacement is required. Moreover, tightening should be done using a torque wrench, since the force should not exceed 20 Nm. The round nuts securing the electrical wire must be tightened by hand only; if hexagonal, use a key (but without pressure). If you apply a lot of force, this will affect the gap (narrow) between the metal body and the glow tube and the spark plug will begin to overheat.
When all of the above checks have shown that the spark plugs are in excellent condition, but when installed on the engine they do not work, then you need to deal with the electrical wiring and the first thing to start with is the fuses, sensors and relays of the glow plugs.
It is better to entrust checking time relays and sensors to specialists. It should be remembered that the heating system only works on a “cold” engine, the temperature of which does not exceed +60°C.
How to check the glow plug relay
Glow plug relay
The diesel glow plug relay is a device capable of activating the spark plugs before starting the engine to warm up the pre-chamber, the activation of which, after turning the key in the ignition switch, is accompanied by a clearly audible click. It itself is not capable of deciding the activation period; this function falls on the ECU, which sends a signal according to the readings of the coolant sensor and the crankshaft sensor. Commands from the block allow you to close and open a circuit.
Check the glow plug relay on a diesel engine if no characteristic clicks. But if the spiral light on the panel stops lighting up, then first inspect the fuses, and then check the temperature sensor.
Each relay has several pairs of contacts (single-component 4, and two-component 8), since there are 2 contacts of the coil winding and 2 more control ones. When a signal is given, the control contacts must close. Unfortunately, there is no universal designation of contacts on relays of different cars; for each relay they can be different. Therefore, we will describe the verification example in general terms. On many diesel cars in the relay, the winding contacts are designated by numbers 85 and 86, and the control ones - 87, 30. So, when voltage is applied to the winding contacts, contacts 87 and 30 should close. And to check this, you need to connect a light bulb to contacts 86 and 87 and apply voltage to the spark plug relay. The light will light up, which means the relay is working properly; if not, the coil is most likely burned out. Relay serviceability glow plugs, as well as the spark plugs themselves, can be check with a tester, measuring the resistance (I won’t say specific indicators, because they vary greatly depending on the model), and if the ohmmeter is silent, then the coil is definitely out of order.
I hope this information will help you in solving your problem, and you can easily figure out how to check the glow plugs of your diesel engine yourself, rather than contacting a service center. After all, as you can see, the test can be carried out not only with the help of a tester, but also with an ordinary car light bulb and battery, literally in a matter of minutes, right in the engine, without unscrewing them from the block.