Glow plugs are a miniature heater, on one side of which there is a heating element, and on the other side - contacts. One glow plug is installed in each combustion chamber. Before starting the engine, the glow plugs are energized and the plugs warm up quickly, raising the temperature in the combustion chamber. The working part of the glow plug is located at the base of the fuel injector. As a result, the injected fuel passes near the glow plug and heats up, which improves the combustion process of the fuel. In addition, small particles of fuel, passing near the glow plug, light up, which improves the ignition process of the fuel.
The duration of the voltage supply to the glow plugs is regulated by the control unit. On early models, the control unit controls the air temperature in the engine compartment. On later models, the control unit controls the coolant temperature based on information from a sensor mounted in the cylinder head. Based on the information received from the temperature sensors, the control unit regulates the timing of the voltage supply to the spark plugs.
The ignition of the control lamp in the instrument cluster indicates the operation of the spark plugs. Within a few seconds, the candles heat up to a high temperature, and the control lamp goes out, which serves as a signal to start the engine. If no attempt is made to start the engine after the warning light has turned off, the timer will cut off power to the glow plugs to avoid draining the battery and overheating the glow plugs. If, on later models, the warning light comes on after starting the engine, there is a problem with the preheating system.
It should be noted that on later models, the glow plugs do not turn off immediately after starting the engine, but after some time, allowing the engine to return to normal operating mode. How long the glow plugs last after starting the engine depends on the temperature of the coolant.
The failure of even one glow plug leads to difficult starting of the engine with interruptions in operation and strong vibration.
Burning and failure of glow plugs are often the result of malfunctioning fuel injectors. If there is a burnt candle, then a simple replacement is not enough. It is necessary to check the nozzles, including determining the shape of the spray cone, the response pressure and tightness. It is important that the injectors have a clear cut-off of fuel.