How to check glow plugs
Content
The task of glow plugs is to heat the air in the combustion chamber of a diesel car as quickly as possible, since the ignition of the mixture, in this case, occurs at a temperature of 800–850 C and such an indicator cannot be achieved by compression alone. Therefore, after starting the internal combustion engine, candles should work until the momentuntil its temperature reaches 75°C.
In relatively warm weather, the failure of one or two glow plugs can be hardly noticeable, but with the onset of cold weather, difficulties immediately appear with starting a diesel engine and the need to check the candles.
Glow plugs
The duration of the current supply to the candle and the magnitude of the voltage are controlled by a relay or a special electronic unit (candles, when glowing up to 1300 degrees for 2–30 seconds, consume current from 8 to 40A each). On the dashboard, a bulb in the form of a spiral shows the driver that it is too early to turn the starter until it goes out. In modern designs, electronics monitor the temperature of the internal combustion engine, and if the engine is warm enough, it does not turn on the candles at all.
A glow plug can fail for two reasons:
- spiral resource exhausted (approximately after 75-100 thousand kilometers);
- fuel equipment faulty.
Signs of broken glow plugs
Indirect signs the presence of a breakdown:
- When starting from the exhaust blue-white smoke. This indicates that the fuel is supplied, but does not ignite.
- Rough operation of a cold ICE at idle. The noisy and harsh operation of the engine can be seen from the shaking plastic parts of the cabin due to the fact that the mixture in some cylinder ignites late due to the lack of heating.
- Difficult cold start diesel. It is necessary to make several repetitions of unwinding the engine starter.
clear signs a bad glow plug will:
- Partial tip failure.
- Fat tip layer near the hull.
- Swelling of the glow tube (occurs due to overvoltage).
How can I check the glow plugs of a diesel engine
How to check?
Depending on the model and age of the car, there are different principles for the 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 successfully start without turning on the glow plugs at freezing temperatures.
Therefore, before proceeding with the diagnosis of the diesel engine preheating system, it is necessary to find out at what temperature regime 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 a diesel engine with ceramic candles, since they have the function of pre-start and post-start heating, which allows afterburning fuel in a cold internal combustion 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, moreover, depending on whether they are unscrewed or on the internal combustion engine, the principle will be the same. The health check can be done using:
3 ways to check glow plugs - video
- battery. On the speed and quality of incandescence;
- saw. After checking the breakage of the heating winding or its resistance;
- Light bulbs (12V). The simplest test for a broken heating element;
- Sparking (can only be used in old diesel engines, since for new ones it is dangerous for the failure of the computer);
- visual inspection.
The simplest diagnosis of glow plugs is to check their electrical conductivity. The spiral must conduct current, its cold resistance within 0,6-4,0 ohms. If you have access to the candles, you can “ring out” 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 (resistance is equal to infinity).
In the presence of a non-contact (induction) ammeter, you can do without removing the candle from the internal combustion engine. But it is often necessary to inspect the working part, on which signs of overheating can be noticeable - melting, deformation of the tip up to its destruction.
In some cases, namely when all the candles fail at once, it may be necessary to check the electrical equipment of the car. Namely, the candle control relay and its circuits.
We will describe all the ways to check diesel glow plugs. The choice of each of them depends on the skills, availability of instruments, tools and free time. But ideally, you need to apply everything together, plus a visual inspection.
How to check glow plugs without unscrewing (for internal combustion engines)
Checking glow plugs should begin with finding out if voltage is applied to them at all, because 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, hold in any way.
For internal combustion engine glow plugs 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 motors you can unscrew the nozzles and look through their wells). Therefore, the most reliable diagnostic option would be to unscrew the candles, check on the battery and measure the indicators with a multimeter, but at least something will do for a quick check.
How to test a glow plug with a light bulb
The principle of checking the glow plug with a light bulb
And so, the first way to check the glow plugs on the internal combustion engine (or already unscrewed) - use of control. Two wires are soldered to a 21 W light bulb (a light bulb of dimensions or stops is suitable), and with one of them we touch the terminal leads of the candles (having previously disconnected the power wire), and the second to the positive terminal of the battery. If the light comes on, then there is no break in the heating element. And so in turn to each candle. When the light bulb glows dimly or does not burn at all — bad candle. Since the method of checking the glow plug with a light bulb is not always available, and its results are relative, the next step is to check with a tester.
Check spark plug
Checking the glow plug for a spark, similar to the previous method, is only done without a light bulb and with intense touches of the threaded part.
To test for a spark, you will need:
- A meter piece of wire, stripped of insulation at the ends.
- Disconnect the spark plugs from the power bus.
- Screw one end of the wire to the "+" battery, and apply the other, with tangential movements, to the central electrode.
- On a serviceable candle, a strong spark will be observed, and on a weakly heated spark, a bad spark will form.
Due to the danger of using this method, it is not used on modern diesel cars, but to know it, at least for how no need to control with a light bulb, definitely!
How to check glow plugs with a multimeter
Checking diesel candles with a multitester can be carried out in three modes:
Continuity of the glow plug with a multimeter for a broken spiral
- in call mode;
- measure resistance;
- find out the current consumption.
Call to break You can even use the heating element without unscrewing the spark plug from the internal combustion engine, but in order to use two other methods of checking glow plugs with a tester, it is desirable that they are still in front of you.
And so, for the dialing mode you need:
- Move the regulator to the appropriate position.
- Disconnect the supply wire from the center electrode.
- The positive probe of the multimeter is on the electrode, and the negative probe is to touch the engine block.
- There is no sound signal or the arrow does not deviate (if an analog tester) - open.
Measuring the resistance of a glow plug with a tester
this method will only help identify a completely inoperative glow plug, but you will not be able to find out problems with the heating element.
Much better to check the resistance with a tester, but for this need to know the value, which should correspond to a specific candle. At good spark plug resistance helix amounts 0,7-1,8 Ohm. Since quite often the candles, although they also work, 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 candle, and without unscrewing it from the diesel engine, you can find out checking current consumption.
To measure, you need: 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 output of the spark plug. We turn on the ignition and look at the indicators of the current consumed. Current consumption of a working candle incandescent, depending on the 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 gradually begin to fall until the current stabilizes. The arrow or numbers on the tester should decrease, without jerks, evenly. All tested spark plugs with internal combustion engines must have the same values of the flowing current. If it is different on some candle or nothing happens at all, then it is worth unscrewing the candle and checking the glow visually. When the candle glows partially (for example, the very tip or middle), the readings will differ significantly, and when it is broken, there is no current at all.
In this case, as with resistance measurements, it is desirable to know the nominal values of current consumption.
When there is no time to produce a test light or tools for extracting candles, or they are already on the table, it can be useful to check with a multimeter. But it also has its drawbacks - this method, like, and 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 candle will not warm up the combustion chamber enough. Therefore, to determine the speed, degree and correctness of incandescence, as well as in the absence of devices at hand, it is imperative to check the candles for heating with a battery.
Checking glow plugs with a battery
The most accurate and visual picture of the health of the heating elements is given by a battery test. Each candle is checked separately, and the degree and correctness of its glow can be seen.
The principle of checking the glow plug with a battery
To check, you need nothing at all - literally a piece of insulated wire and a working battery:
- We press the central electrode of the candle to the positive terminal.
- We connect the minus to the body of the heating element with a wire.
- Rapid heating to red (and it should be heated from the tip) indicates serviceability.
- Slow glow or his no - candle is faulty.
For a more accurate test, it would be a good idea to measure the rate at which the tip of the candle heats up to a cherry color. Then compare the heating time of each candle relative to the others.
Those candles that heat up earlier or later from the base group (the average time for modern candles is 2-5 seconds) are put aside for scrap. Ask why those that used to be thrown away, is it good? When the candles are of the same brand and of 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, cracks on the body are very often observed in these places. So when testing for heating, it is desirable to know the characteristics of the candles or take the values of the new one as a standard.
When the candles, although they work, but warm up to different temperatures and at different speeds, then, as a result, ICE jerks occur (one already ignites the fuel mixture, and the other only burns after it). Quite often, they can check all the candles at once at the same time, connecting them not in series, as it would seem, but in parallel, then everyone will receive the same current strength.
The only difficulty with this method is that you have to unscrew all the candles, and this sometimes turns out to be quite difficult and time-consuming. But the plus is also that in addition to checking for heating of glow plugs, at the same time we check for a hidden defect.
Visual inspection of glow plugs
A visual inspection 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 candle
If the candles have not yet run out of their resource, but already have traces of overheating (approximately in the middle of the heated rod), the body swells and cracks scatter on the sides, then this is:
- Too high voltage. It is necessary 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 click time or check the relay with an ohmmeter.
Melting the tip of the candle
It can happen for reasons:
- Early injection of the fuel mixture.
- Dirty nozzles, resulting in incorrect spraying. You can check the injection torch on a special stand.
- Weak compression and late ignition, and, accordingly, overheating.
- Pressure valve closed. Then the motor will work hard enough, and if you loosen (on a running engine) the nut of the fuel line leading to the nozzle, then not fuel will come out from under it, but foam.
When visually checking the thinnest part of the candle (the one that is in the prechamber), look for it to be darkened, but not with a melted iron body, and without cracks. Because even if it works as well, it will not last long, and soon you will have to check its work again.
By the way, the poor performance of the candle can happen due to insufficient contact with the supply bus. With a weak tightening of the nut due to vibration, it is slightly unscrewed. But you should not pull too hard, you can damage the electrode. Often candles are damaged by unprofessional actions when twisting / twisting. It is not uncommon that incorrect torque applications can lead to loss of compression, and their vibration destroys the core in ceramic glow plugs.
Glow plugs - enough fragile, so it is advisable to unscrew them from the internal combustion engine only if replacement is required. Moreover, tightening should be done using a torque wrench, since the force must not exceed 20 Nm. Round nuts for fixing the electric wire are tightened only by hand; if hexagonal - with a key (but without pressure). If you apply a lot of force, this will affect the gap (narrow) between the metal case and the glow tube and the candle will begin to overheat.
When all of the above checks showed that the candles are in excellent condition, but when installed on an internal combustion engine, they do not work, then you need to do electrical wiring and the first thing to start with is fuses, sensors and glow plug relays.
How to test the glow plug relay
Glow plug relay
The diesel glow plug relay is a device capable of activating the spark plugs before starting the internal combustion engine to warm up the prechamber, the activation of which, after turning the key in the ignition switch, is accompanied by a clearly audible click. It itself is not able to decide the activation period, this function falls on the computer, which sends a signal according to the indicators of the coolant sensor and the crankshaft sensor. Commands from the block allow you to close and open the circuit.
Check glow plug relay diesel is in the event that no characteristic clicks. But if the spiral light on the panel has stopped 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 coil winding contacts and also 2 control contacts. When a signal is applied, the control contacts must close. Unfortunately, there is no universal designation of contacts on the relays of different cars, for each relay they can be different. Therefore, we will describe an example of verification in general terms. On many diesel vehicles in the relay, the winding contacts are indicated by the numbers 85 and 86, and the control ones are 87, 30. So, when voltage is applied to the winding contacts, contacts 87 and 30 must close. And, in order to check this, you need to connect a light bulb to pins 86 and 87, apply voltage to the candle relay. The light will light up, which means that the relay is working properly, if not, the coil is most likely burned out. Relay health glow plugs, as well as the candles themselves, you can check with a tester, by 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, and not contact the service. After all, as you can see, the check can be carried out not only with the help of a tester, but also with an ordinary machine light bulb and battery, literally in a matter of minutes right in the internal combustion engine, without unscrewing them from the block.
