An ignition spark jumps between the central electrode and the side electrode(s), igniting the fuel-air mixture.
Without good reason, the manufacturer's instructions regarding the type of spark plugs used, which is determined, among other things, by the heat rating, should not be ignored.
The vehicle manufacturer recommends using a specific type of spark plug to ensure the engine runs smoothly.
When removing the spark plugs, you should also follow all the above safety precautions. First of all, disconnect the battery.
When removing the spark plugs, make sure that no foreign objects have entered the holes into which the spark plugs are screwed. Failure to do so will result in damage to the valves, valve seats, or even the cylinder head after the spark plugs are installed and the engine is started.
Based on the appearance of the spark plug, certain conclusions can be made about its functioning, mixture formation and the condition of the engine (pistons, piston rings, etc.).
The spark plug is normal if there is a light powdery coating from gray-yellow to gray-brown on the electrodes and insulator. At the same time, this indicates that the engine is also in order. The glow number of the spark plug in this case is also chosen correctly and corresponds to the operating loads.
If the spark plug body, insulator and electrodes are covered with a thick layer of powdery black-gray soot (carbon deposit), this means that the mixture formation is adjusted incorrectly and the air-fuel mixture is oversaturated. The air supply is too low, the throttle opening time is too long, the gap between the electrodes is too large, the glow number of the spark plug is too high and its temperature during engine operation is below the required operating temperature.
The presence of oily carbon deposits on the insulator, electrodes and spark plug housing indicates that engine oil is getting into the combustion chamber. This may be due to wear of the pistons or piston rings.
The presence of dark brown or even grey-black glassy, stuck deposits on the insulator, which sometimes have the shape of drops, with simultaneous damage to the electrodes, especially the central one, and the spark plug body, is evidence of a lean mixture, a loosely tightened spark plug, poorly closing valves. The spark plug itself may be the cause, because its heat rating does not correspond to the engine's needs.
[Information posted on the website: peugeotbook.ru]
The glow number shows the degree of heat load on the spark plug that it can withstand. The lower the glow number of the spark plug, the higher its ability to withstand heat loads. Such a spark plug removes heat better, preventing detonation combustion. A spark plug with a high degree of heat resistance has its own drawback - it needs a high self-cleaning temperature. Therefore, such spark plugs quickly become covered with carbon deposits, especially in conditions when the engine does not reach its operating temperature during movement (movements in urban conditions, short distances in winter).
It is recommended to remove deposits that accumulate between the insulator and the central electrode using a sand jet from a spark plug tester. Before installing the spark plugs, it is essential to clean their threads.