The function and characteristics of spark plug: the function of spark plug is to introduce the pulsed high voltage electricity produced by the ignition coil to the combustor, and to ignite the mixture by the electric spark produced by the electrode to complete the combustion. The model of the domestic spark plug is made up of three parts of numbers or letters. The front number represents the thread diameter, such as the number 1, indicating that the thread diameter is 10mm, the middle letter indicates the length of the spark plug into the cylinder part; the last digit indicates the hot type of the spark plug: 1-3 is the heat type, 5, 6 is medium, and more than 7 is cold type. The "gap" of the spark plug is the main technical index of the spark plug. The gap is too large. The high voltage electricity produced by the ignition coil and the distributor is difficult to jump through, which makes it difficult to start. If the gap is too small, the spark will be weak and the leakage is easy to happen at the same time. How to check the spark plug of the car: 1, dismantling: remove the high voltage line on the spark plug in turn and mark it in the original position so as not to install the dislocation. In the demolition, pay attention to clearing the dust and debris in the spark plug hole in order to prevent debris from falling into the cylinder. When using the spark plug sleeve, the spark plugs should be held down and the sleeves should be rotated and discharged. 2. Check: the normal color of the spark plug's electrode is grey and white, such as blackening of electrode and carbon deposition. During the inspection, the spark plug can be connected with the cylinder body, and the terminals of the spark plug can be touched by the central high voltage line, then the ignition switch is switched on to observe the position of the high voltage electric jump. If the electric jump position is in the gap of the spark plug, it indicates that the spark plug works well, otherwise, it needs to be renewed. Adjustment of spark plug gap: there are differences in spark gap between different models, generally 0. 7-0. 9, check the gap size, using spark plug gauge or thin sheet metal. If the gap is too large, the outer electrode can be knocked lightly with the handle of the child, so that the gap is normal; when the clearance is too small, the electrode can be inserted into the electrode to move outward. Replacement of spark plugs: spark plugs are expendable parts and should normally be replaced by 20000-30000 kilometers. The mark of the spark plug replacement is that it does not jump fire, or the discharge part of the electrode is circular due to ablation. In addition, it is found that the spark plug is often accumulated and broken in use, usually because the spark plug is too cold to be replaced by a hot spark plug. If there is a hot ignition or a shock sound, a cold spark plug is needed. Cleaning of spark plugs: spark plugs should be cleaned in time for oil contamination or coke deposition, but not barbecue with flame. If the porcelain core is damaged or broken, it should be replaced.