Glow Plug Relay for different automobiles
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Your Glow Plug Relay worn out? » Read more about common malfunctions • Repair • Replacement manual
Starting the diesel engine with the glow plug
Glow plugs are indispensable for the cold start of a diesel engine. They provide the preheating of the combustion chamber, enabling the ignition process of the diesel engine. For the proper function of the glow plugs, a separate control unit is required.
Difference between a diesel and a petrol engine
The important difference between a petrol and a diesel engine is its ignition. Where in a petrol engine every process requires a separate ignition, diesel engines are so-called self-igniters. This means that the injected fuel independently provokes combustion under sufficient pressure. Diesel engines require a higher working pressure than petrol engines. In a self-igniting engine a pressure of 180 bar. is common, where petrol engines only reach 75 bar. This high internal pressure only occurs under ideal conditions: the engine must be sufficiently heated and all metal parts must be allowed to expand as foreseen in order for a diesel engine system to be sufficiently tight to withstand this high internal pressure. Furthermore, a diesel engine has a low combustion temperature due to its degree of efficiency. It needs a longer time to heat up. Especially in the cold season, glow plugs are indispensable for the function of a diesel engine.
Task of glow plugs
Glow plugs consist of a heat-resistant metal stick. Often carburised iron is used. This stick is put under high voltage, causing it to glow. The injected diesel is ignited by the glow plug without reaching its self-ignition. When the motor is sufficiently heated, the glow plug switches itself off and the diesel flows independently. The automatic glowing process is controlled by the glow-time control unit.
Task of the glow-time control unit
In the early age of diesel technology, glow plug control was done with simple bi-metal switches. These were very imprecise and wore out quickly. In order to realise a punctual control of the preheating time, nowadays the professional glow-time control unit is used. It controls the voltage, maximum temperature, the preheating time and the effective afterglow duration. The control unit has a measuring task apart from its control functions. If the glow-time control unit detects a deviation from the actual value, it can respond to the imminent glow plug failure and relay it to the error memory.
Defects of the automatic preheater
The glow-plug control unit is an electronic part and sensitive to moist. Generally, malfunctions are reported to the engine control and given a corresponding error code. The most obvious symptom of a defective control unit is a non-starting car. In most cases only the fuse is defective. The high start-up currents must be secured in order to prevent cable fires.
If the automatic preheater becomes brittle and cracked due to old age, it needs to be replaced. This is really easy. It is a simple plug-in module, which can be simply removed and replaced by a new one. It is recommended to replace the glow plugs along with the control unit. This guarantees the new condition of the entire preheating system of the diesel engine. Buying a glow-time control unit Although it is a technically complex device with an important task, the glow-time control unit is amazingly cheap in purchase. Prices begin, depending on manufacturer and vehicle, at ca. 50 euro (£43). In spite of the simple replacement, many cars require a visit to the garage: the error memory must be deleted and adjusted to the new automatic preheating. This is, however a matter of minutes. Generally, a glow-time control unit defect represents a manageable project, which can be executed with the common mechatronic skills.