It is possible to check the candles for electrical conductivity only in the installed state, therefore, a special control device with an LED is used for this. It is better to entrust the check of candles to the specialists of the service station.
If carbon deposits are found on the turned out candle, this most likely indicates a malfunction of the nozzle. An inaccurate injection start time also affects the life of the spark plugs. When buying spark plugs, always match them by engine type and year of manufacture.
Spark plug failure is usually noticeable when starting a cold engine. The fuel in the cylinder with a working spark plug will ignite, with a faulty spark plug, ignition will occur with a delay. Rough running engine and blue exhaust also indicate a bad spark plug. To access the candles, you must first remove a number of parts.
Pic. 171. The electrical circuit of the engine preheating system: 1 - relay for turning on glow plugs; 2 - signal lamp in the instrument cluster; 3 - central switchgear; a, d - relay; b - electronic unit; c - temperature sensor; G - glow plugs; M - connection with «weight»
On the electrical diagram in Fig. 171 it can be seen that the preheating device consists of glow plugs, a relay for regulating the time of the glow plug and a warning lamp in the instrument cluster. When the ignition is turned on, the current through the relay is supplied to the terminal «15». Relay a supplies voltage from the phase terminal «30» through the fuse (80A) on candles. The voltage supplied to the plugs is a minimum of 11.5 V at a current strength of about 30 A, which is reduced by the installed regulator to 8-15 A to prevent the candles from burning out. Within 10 seconds, the candles heat up to approximately 900°C, after 30 seconds the glow temperature can rise to 1180°C.
The relay regulates the operating time of the candles. It is controlled based on information from the outside temperature sensor. The lower the outside temperature, the longer the candle life. At -30°C it can be, for example, 25 seconds, in summer it is reduced to 2 seconds. When the candles stop working, the control lamp in the instrument cluster goes out. If the engine does not start immediately with the ignition on, the safety device cuts off the voltage supply to the spark plugs. When the engine is started, the preheating is switched on again. It happens through the terminal «50» starter.
The candle can burn out from high temperature. Spark plugs can fail due to injector malfunctions, incorrect injection timing, or injection pressure that is too low. In this case, the spark plugs must be removed and replaced. When replacing, you should once again make sure that they are suitable for this engine.