For this purpose, a glow plug is screwed into each combustion chamber. It consists of a housing with a heating rod pressed into it. When voltage is applied, the heater coil in the rod heats up to a temperature of over 850°C within a few seconds, resulting in a preheating period rarely lasting more than 10 seconds. Once the preheating indicator lamp in the instrument cluster turns off, the engine can be started.
To speed up engine warm-up, on models produced since 1987, preheating continues after engine start-up. The heating duration is determined by the control unit depending on the coolant temperature. The control unit is located behind the center console under the air duct. Information about engine temperature is received by the control unit from the coolant temperature sensor. Based on the received data, the control unit determines the duration and strength of the current.
Checking the engine preheating system
If you have difficulty starting the engine, first measure the compression in the engine cylinders. If the compression is too low, the engine will not start at low ambient temperatures.
Checking glow plugs
Loosen the nuts and disconnect the wires from the glow plugs.
Figure 4.17. Using an ohmmeter to measure the resistance between the glow plug contact and the cylinder block
Connect an ohmmeter in series to each glow plug and check the resistance between the glow plug contact and the cylinder block (figure 4.17).
If the resistance is not zero, the glow plug is faulty and must be replaced.
Figure 4.18. Glow plug: 1 – nut with washers; 2 – connecting wire; 3 – candle
Remove the faulty glow plug. Screw in a new glow plug and tighten it to 20 Nm (figure 4.18).
Connect the wire to the glow plug and secure it with a nut and washers.
Caution! Do not exceed the specified tightening torque, as this may damage the glow rod and cause premature spark plug failure. Make sure that no oil or fuel comes into contact with the glow plug.
Glow plugs with burnt heating rods
Figure 4.19. Glow plug with a burnt rod
Burning of glow plug rods (figure 4.19) is often a consequence of faulty fuel injectors. Such damage should not be classified as internal or external defects of the glow plug.
Text taken from an online platform: MAZBOOK.ru
Caution! If damage is not detected and the engine starts poorly, inspect the glow plugs visually with the preheater on. To do this, remove the fuel injectors and observe the glow plugs through the holes during warm-up.
If such glow plugs are detected, it is not enough to simply replace them. In this case, it is also necessary to check the fuel injectors for injection pressure and tightness.
Checking the glow plug relay
Figure 4.20. Connecting the glow plug relay to the battery terminals and checking the relay contact closure
Disconnect the glow plug relay connector. Using two additional wires, connect the relay to the battery terminals as shown in the figure 4.20, and check if the relay contacts close.
If the relay contacts do not close, replace the relay.