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 winding in the rod heats up to a temperature above 850°C within a few seconds, as a result of which the duration of heating before starting rarely lasts more than 10 s. When the preheat indicator lamp in the instrument cluster goes out, the engine can be started.
To speed up the warm-up of the engine on models from 1987, preheating continues after the engine is started. The duration of heating is determined by the control unit depending on the temperature of the coolant. The control unit is located behind the center console under the air duct. Information about the engine temperature enters 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, then at low ambient temperatures the engine will not start.
Checking glow plugs
Remove the nuts and disconnect the wires from the glow plugs.
Pic. 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 (pic. 4.17).
If the resistance is not zero, the glow plug is bad and needs to be replaced.
Pic. 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 (pic. 4.18).
Connect the wire to the glow plug and secure it with a nut and washers.
Attention! Do not exceed the specified tightening torque as the glow plug may be damaged and the spark plug will fail prematurely. Make sure that no oil or fuel gets on the glow plug.
Glow plugs with burnt heating rods
Pic. 4.19. Glow plug with burnt core
Burning of glow plugs (pic. 4.19) often the result of a faulty fuel injector. Such damage should not be attributed to internal or external defects of the glow plug.
Attention! If no damage is found and the engine does not start well, visually inspect the glow plugs with the preheat on. To do this, remove the fuel injectors and watch the glow plugs through the holes as they warm up.
If such glow plugs are found, it is not enough to replace them. In this case, it is also necessary to check the fuel injectors for injection pressure and tightness.
Checking the glow plug relay
Pic. 4.20. Connecting the glow plug relay to the battery terminals and checking the relay contacts for continuity
Disconnect the glow plug relay connector. With two additional wires, connect the relay to the battery terminals, as shown in fig. 4.20 and check if the relay contacts close.
If the relay contacts do not close, replace the relay.