First, learn to distinguish abnormal sound that belongs to reasonable sound.
It is difficult for ordinary car owners to distinguish between faulty abnormal noise and reasonable abnormal noise. When I went to the repair shop to check the vehicles with abnormal sound, only nearly 20% of the vehicles really had problems. There must be a difference between the sound of a turbocharged engine and that of a naturally aspirated engine. Vehicles with engine guards may also generate noise due to friction; After some car owners come into contact with different cars, they may mistake reasonable abnormal noise for vehicle failure because of their lack of understanding of mechanical knowledge. Therefore, learn to distinguish the abnormal sound of cars and avoid wasting time and energy.
Second, the identification method of car noise:
In practical work, due to the limitation of working conditions, it is difficult to measure the noise of cars with special instruments, so we can only describe and compare the noise of cars by judging the sound in daily life. For example, the "clatter" sound caused by dry friction of bearings, and the "click" sound similar to a small hammer tapping the cement floor caused by excessive valve clearance.
1, correctly distinguish normal noise from abnormal noise.
The vibration of various mechanisms when the car is working will make noises of various properties, but the noise does not mean that the car is faulty. In order to avoid unnecessary disassembly, it is necessary to distinguish between normal noise and abnormal noise. The normal vibration sound of each system component (such as the noise on the engine surface), the impact sound of gears during gear shifting, the intake sound and exhaust sound using gas as the working source, and the gear meshing noise are all normal noises. Abnormal noise (abnormal noise) can be divided into slight noise, general noise and malignant noise according to its influence on automobile performance. Slight noise, such as high-voltage electric leakage flashover noise, rolling bearing slightly loose noise, etc., is generally low in volume, and the degree of wear of parts is not great, and there is no significant change for a long time. This kind of fault can still maintain the normal running of the car without repair.
3, in the diagnosis of abnormal car noise, should pay attention to create good auscultation conditions, try to eliminate the interference of other noise, so as not to affect the accuracy of judgment.
It is best to amplify or reduce the sound consciously, that is, use a screwdriver or other metal bar as the sounding part of the stethoscope to amplify the sound, or use a single cylinder to cut off the fire to reduce the sound to meet the needs of diagnosis. The auscultation site should be kept quiet to minimize the interference of human factors.
Third, below we list some common and easy-to-eliminate automobile abnormal sounds and simple ways to distinguish and eliminate them.
1, abnormal sound on the body.
Symptoms: There are always some abnormal noises in a certain part of the car body when driving on the accelerator or braking, which are not loud and do not affect normal driving, but people are always a little worried about what is wrong.
Analysis problem: This problem usually occurs because the rigidity of the car body is not enough, which leads to the deformation of the vehicle during driving, the friction or jitter between the door and the frame, or the friction between the steel plates caused by the desoldering in some places.
There are also some cars with large wind noise, which is related to the shape of the car to a certain extent. There are also some cars whose body parts are not fixed properly, which may also cause abnormal noise, which can generally be solved by tightening the screws.
Solution:
First of all, check whether there are objects that are not fixed, easy to roll and make noise in the trunk or rear seat of the car, and eliminate the noise caused by some items that are not fixed properly.
If it is found that abnormal noise is caused by friction on the doors and windows, you can stick rubber strips on the doors and windows or pad rubber on the friction parts, which may reduce or eliminate the abnormal noise, but the result is only a temporary solution, not a permanent cure. If the above problems are not found, you must go to a regular repair shop for maintenance and troubleshooting.
2. The engine has abnormal sound.
Symptom Description: There are many possibilities of abnormal noise in the engine compartment. Most people also judge that it is abnormal noise in the engine compartment based on the sound source, usually it is metallic harsh noise or wind whistling noise.
Analysis of the problem: abnormal noise from the engine compartment, there will be more harsh belt howling, which is generally caused by belt slipping; There will also be a sharp sound of dry friction of metal parts when the engine is running, which is generally the reason for the damage of bearings of generators, water pumps and steering booster pumps; If it is the sound of air leakage from engine operation, it may be the result of blockage of exhaust system, leakage or fracture of vacuum tube.
Solution: The abnormal sound of the engine indicates that the technical state of a certain mechanism of the engine has changed. Mainly because some parts are worn or even improperly assembled and adjusted. Some abnormal sounds can predict that the engine may be damaged accidentally, so when the engine has abnormal sounds, it should be repaired in time to prevent the fault from expanding.
Need to be reminded that if it is an abnormal sound in the engine, most of the owners can't solve it by themselves, so it is best to send it to the factory for maintenance.
3. The gearbox has abnormal sound.
Symptoms: If there is a "rustling" sound inside the gearbox when the car is driving, but it is gone after stepping on the clutch or accelerator, there will be a whistling sound when shifting gears.
Analysis problem: if the noise source encountered during driving is the gearbox, it may be caused by the wear of gearbox bearings or gears and bearing spots. Abnormal sound of gearbox during speed-up shifting may be caused by metal powder contained in gearbox oil, indicating excessive wear of parts such as brake band clutch in gearbox.
4. The tire has abnormal sound.
Symptom Description: The tires make a rhythmic noise, and the faster the vehicle speed, the higher the frequency.
Analysis: When automobile tires touch the ground, they will produce various noises with different strengths due to the type of road or the concave-convex state, the speed of the automobile, the type of tires and the air pressure of the tires themselves. Therefore, no matter how perfect the car is, it cannot completely eliminate the noise generated by tires and the ground during driving.
5. The engine guard plate has abnormal sound.
Symptoms: The engine fender has been installed for some time, but after going out to run some suburban road conditions, there is a strange noise at the fender when I come back.
Solution: The screw often moves in the car that moves frequently. If you often hear an abnormal sound like "rattle" from the position of the air intake grille, besides the grille is really loose, then the owner should check whether the engine fender screw is loose, or the engine fender and the negative film are loose, resulting in abnormal sound. Besides fastening the screw, you should also pad some cardboard items at the abnormal sound position, so that the abnormal sound can be easily eliminated.
6. The brakes have abnormal sound.
Symptoms: The vehicle makes loud noise and abnormal sound when stepping on the brakes.
Analysis: Of course, abnormal noise during braking may be caused by other reasons, such as improper use or deformation of brake disc material, unqualified hardness, porosity, friction characteristics and compression characteristics of brake friction disc, rust of brake friction disc and brake disc due to moisture, too hard metal wire in brake friction disc formula, and scraping of mechanical brake friction disc. To solve this phenomenon, you only need to brake hard for several times to relieve abnormal sound.
6. The brakes have abnormal sound.
Symptoms: The vehicle makes loud noise and abnormal sound when stepping on the brakes.
Analysis: Of course, abnormal noise during braking may be caused by other reasons, such as improper use or deformation of brake disc material, unqualified hardness, porosity, friction characteristics and compression characteristics of brake friction disc, rust of brake friction disc and brake disc due to moisture, too hard metal wire in brake friction disc formula, and scraping of mechanical brake friction disc. To solve this phenomenon, you only need to brake hard for several times to relieve abnormal sound.
Solution:
Brake friction plate is one of the most important parts in the brake system. Generally, the service life of the front brake friction plate is 30,000 km, and the service life of the rear brake friction plate is120,000 km. If there is a "squeak, squeak" sound when braking, it is mostly a warning sound issued by the wear indicator of the brake friction plate, which indicates that the brake friction plate exceeds the service limit. When this happens, car owners should go to the car dealership for maintenance as soon as possible, otherwise the brake friction plates will be exhausted, resulting in brake parts damage, abnormal braking effect and accidents.