Bi Ye's thesis
Discussion on Fault Analysis and Diagnosis Method of Jetta Car
Last name: Li
Student ID 20077 1 10550225
Use and Maintenance of Special Purpose Vehicle
Grade 07 autumn class
Instructor Ren Huiqiao
April 28(th), 2009
catalogue
Directory 1
[Abstract] 2
1. Introduction 3
2. Fault analysis of high water temperature 2V of Jetta 3 car.
2. 1 Check engine cooling system 3
2.2 Check the electronically controlled cooling system 4
2.3 Check the water temperature monitoring system 5
3. Engine abnormal sound fault and analysis 5
3. Analysis of Abnormal Noise Characteristics of1Engine 5
3.2 Diagnosis of Abnormal Engine Sound 7
3.2. 1 Diagnostic principles of abnormal sound 7
3.2.2 Abnormal sound diagnosis method 7
3.2.4 Example analysis
4. Summary 9
[References] 9
[Abstract]
Taking the common faults of Jetta as the theme, this paper introduces the EFI engine of Jetta. Aiming at the common faults of Jetta cars, such as high water temperature and abnormal engine noise, theoretical analysis and diagnosis methods are carried out, especially the detailed diagnosis method of abnormal engine noise.
[Keywords:] Jetta; Fault analysis; case analysis
Discussion on Fault Analysis and Diagnosis Method of Jetta Car
1. Introduction
Jetta is equipped with 1.6L gasoline electronically controlled injection engine, which has few faults, and the computer storage function of accidental faults makes the engine doomed even if it changes slightly. Compared with carburetor engine, electronically controlled gasoline injection engine has the outstanding advantages of accurately controlling the quality of mixture, ensuring the complete combustion of fuel in the cylinder, reducing exhaust emission and fuel consumption, and at the same time improving the charging efficiency of the engine and increasing the power and torque of the engine. The disadvantage of electronically controlled fuel injection device is that the cost is a little higher than that of carburetor, so it is more expensive. Although the failure rate is low and it is difficult to repair once it is broken, these shortcomings are insignificant compared with its operation economy and environmental protection. The fuel injection passage is composed of electric oil pump, fuel filter, oil pressure regulator and fuel injector. The command signal sent by the electronic control unit can open the injection head and inject fuel. The sensor specially receives values such as temperature, mixture concentration, air flow and pressure, crankshaft speed, and transmits them to the electronic control unit. The electronic control unit is a computer with integrated circuits and other complex electronic components. It collects the signals collected by various sensors on the engine and the signals of the ignition distributor, quickly analyzes and calculates the fuel supply for the next cycle, and sends an injection instruction to the fuel injector in time, so that the fuel and air form an ideal mixture and enter the cylinder for combustion to generate power.
2. Fault analysis of high 2V water temperature of Jetta car.
2. 1 Check the engine cooling system
(1) The outside of the water tank is dirty or the air conditioner condenser is blocked with the water tank. , resulting in poor heat dissipation of the water tank and high water temperature. Clean up if necessary. To clean the radiator, first remove it, spray the surface with the external cleaning agent of the engine several times, rinse it with clean water after a few minutes, and dry it with a high-pressure air gun. The outer surface of the condenser is also immediately cleaned with external cleaning agent.
(2) The thermostat is damaged and can't be opened, so that the coolant can't smoothly enter the water tank to form a large cycle, and the water temperature rises rapidly, leading to boiling. The thermostat decides whether to adopt "cold cycle" or "normal cycle". The thermostat opens when the water temperature rises, and the higher the temperature, the greater the opening. If the thermostat is not closed, the cycle will enter the "normal cycle" from the beginning, resulting in the engine not reaching the normal temperature as soon as possible. The thermostat can't be opened or it can't be opened flexibly, which will make the coolant unable to circulate through the radiator, which will cause the temperature to be too high or too high. When the thermostat can't be opened, the temperature and pressure of the upper and lower pipes of the radiator will be different.
(3) The water pump is damaged, and the coolant can't be sent into the water tank, resulting in poor coolant circulation and high water temperature until the pot is boiled. Need to repair or replace a new water pump. As for the water pump, when the timing belt of Jetta car is changed for 80,000 kilometers, it is necessary to check whether the water pump has any signs of leakage, and replace it if it leaks. Please carefully check one side of the timing belt for signs of water leakage. For Jetta cars with mileage exceeding1.2000 km, the owner is advised to replace the water pump when replacing the timing belt. For Jetta cars with long mileage, the shaft and blades are easy to separate, so we must pay attention to maintenance.
(4) Too much scale in the water tank and engine water jacket will also cause poor heat dissipation and increase the water temperature. Clean the waterway if necessary. Clean the waterway, remove the thermostat and flange, and check whether the thin water pipe at the return pipe-throttle body-expansion water tank on the cylinder head is unblocked. If it is not unblocked, try to deal with it.
(5) Insufficient antifreeze and too little coolant can also cause the water temperature to be too high, so it is necessary to add or replace the coolant in time. Due to the irregular addition and replacement of antifreeze, the engine water channel and water tank will be blocked in advance, resulting in excessive water temperature. Antifreeze should be replaced once every two years, and original fittings must be used when replacing and adding. If the concentration is too high, the heat dissipation effect will be poor and the engine will overheat. This harm is not obvious when the engine is running at low load, and the coolant temperature will be too high when it is running at high load and high speed. Therefore, it is not allowed to add antifreeze solution at will, and the concentration must be detected first. Different kinds of antifreeze cannot be mixed for use, so as not to cause chemical reaction, produce precipitation or bubbles, and reduce the use effect; When replacing antifreeze, start the engine first, then stop the engine and release the cleaning liquid. Add clean water to the cooling system, idle for 10 minute, then drain water, and repeat several times until clear water flows out of the waterway, and then add new antifreeze and water.
(6) There is air in the cooling system, which causes the cooling water not to circulate normally.
(7) The cylinder gasket is damaged, which causes the high-temperature and high-pressure gas in the cylinder to enter the cooling system, so that the water temperature quickly rises to boiling. A new cylinder liner must be replaced. The cylinder pads of the new two valves are made of steel plates. Generally, short-term high water temperature will not burn the cylinder gasket, but it will be damaged if it is not cooled for a long time.
(8) For the high water temperature of the engine, it must be checked under the condition of ensuring that all parts of the cooling system have no leakage. The water leakage part includes the three-way water pipe, water pump, water pipe joint, radiator, thermostat, cylinder gasket and liquid storage pipe cover behind the cylinder head. In the case of leakage, be sure to use a tester to pressurize after finishing and observe whether there is leakage in each part.
2.2 Check the electronic cooling system.
Jetta's cooling fan is electrically controlled. Generally, the water temperature is within 100 degrees, and the electronic fan rotates at a low speed. When the water temperature is generally above 100 degrees, the electronic fan runs at high speed. When the air conditioner switch is turned on, the electronic fan will also run at a low speed. The causes of high water temperature caused by electric control system are:
(1) Check that the cooling electronic fan does not turn, or there is no high or low gear, which makes the forced air cooling of the electronic fan invalid, resulting in high water temperature. If necessary, replace the electronic fan.
(2) Double temperature switch failure. The two-temperature switch has two switches: one is to turn on the fan at about 90 degrees to make it run at a low speed, and the fan stops below 84 degrees; The second is to turn on the fan at about 100 degrees, so that the fan can run at high speed and enhance its heat dissipation ability. When the water temperature drops to 90 degrees, the fan runs at a low speed. When testing, use a multimeter to test whether the two-speed switch is closed or unplug the two-temperature switch at the corresponding temperature, short-circuit the two plugs, and observe whether the fan is running. If so, and the fan connected to the plug does not work, it means that there is something wrong with the switch and it must be replaced with a new one.
(3) The electronic fan is controlled by the relay, and the damage of the relay causes the electronic fan not to operate, and there is no forced air cooling, so the water temperature is high.
(4) The air conditioning relay is damaged. Turn on the air conditioner switch, and the electronic fan must run at a low speed regardless of the cooling water temperature; When the air conditioning system pressure exceeds a certain value, the electronic fan should also run at high speed. If it is not normal, check the air conditioning control system. Appropriate amount of snow in the air conditioner, too high pressure at the high-pressure end of the air conditioner system, too much refrigerant or refrigeration lubricant, too high pressure due to the failure of the self-regulating function of the internal self-regulating air conditioner compressor, and blockage of the air conditioner condenser will increase the load of the engine, consume the heat dissipation performance of the cooling system, and lead to too high water temperature. In addition, too little or too much refrigerant will reduce the refrigeration effect.
2.3 check the water temperature monitoring system
If there are no problems in the above two aspects, there will generally be no problems of high water temperature and boiling, and the rest is the problems of water temperature monitoring system, such as the water temperature meter showing that the water temperature is too high or too low, which leads to false alarm. The failure causes of the monitoring system may include:
(1) The water temperature sensor is damaged. Poor grounding of the negative electrode sometimes changes the resistance value of the sensor, and the signal is inaccurate. Grounding points: the negative wire on the battery, the grounding wire under the battery and the car body, the grounding point on the wave box, the grounding point on the cylinder head and the grounding point behind the central relay box. If necessary, replace the engine small head harness.
(2) If the display of the water thermometer is abnormal, you can use a special measuring tool to detect the measuring base point and range of the water thermometer. If it is not normal, you need to replace the water thermometer.
(3) Under normal circumstances, if the regulated output voltage is too high or too low, it will also make the water thermometer display inaccurate, which may show that the water temperature is too high, and even the alarm light will light up.
(4) Some Jetta cars have two similar plugs, both of which are like water temperature sensors. One is a water temperature sensor and the other is an intake manifold heating control switch. If the two plugs are inserted backwards, the water thermometer will also display an error.
(5) The failure of the circuit itself will also make the thermometer display wrong. In general, the maximum resistance of circuit connection should not exceed 0.5 Ω.
Through the above comprehensive inspection, the faulty vehicle is caused by the high water temperature of the vehicle due to the failure of the thermostat. I learned some skills from my tutor during my internship at FAW-Volkswagen.
3. Engine abnormal sound fault and analysis
The abnormal sound of the engine indicates that the technical state of the engine mechanical device has changed. The main reason is that some parts are worn or even improperly adjusted. Some abnormal sounds can indicate that the engine may be accidentally damaged, so when the engine has abnormal sounds, it should be repaired in time to prevent the fault from expanding. Before disassembly, it is necessary to check and determine the fault position, and then analyze the abnormal noise characteristics of the engine, so that the position, cause and degree of abnormal noise can be basically diagnosed and the blindness of disassembly inspection can be avoided.
3. 1 Analysis of abnormal noise characteristics of engine
Engine abnormal sound is often related to engine speed, load, temperature and working cycle. By analyzing the characteristics of abnormal sound, we can find out its changing law.
(1) Relationship between Abnormal Noise and Engine Speed
The existence of the most common abnormal noise of the engine depends on the speed state of the engine. Abnormal sound only exists at idle speed or low speed. The causes of noise are: the gap between piston and cylinder wall is too large; The piston pin is assembled too tightly or the connecting rod bearing is assembled too tightly; The gap between tappet and its guide hole is too large; Wear of valve cam profile; Sometimes the starting grip is loose, which will make the pulley ring (obviously when shifting).
(2) the relationship between abnormal sound and load
Many abnormal noises on the engine are obviously related to its load, and the relationship between abnormal noises and load can be determined by reducing the load one by one in diagnosis.
(3) the relationship between abnormal sound and temperature
As the temperature rises, the sound will decrease or even disappear. The causes of noise are: the gap between piston and cylinder wall is too large; Due to the depth and width of the main bearing oil groove, the piston is misaligned; Low oil pressure and poor lubrication. There is noise after the temperature rises, and the noise decreases or disappears after the temperature drops.
(4) Relationship between abnormal sound and engine working cycle
The abnormal noise of the engine is often obviously related to the working cycle of the engine, especially the abnormal noise of the crank-connecting rod mechanism and the valve train is related to the working cycle.
(5) Relationship between abnormal sound and engine position
When the engine has abnormal sound, it will inevitably produce some vibration. According to the characteristics and location of vibration, the cause of abnormal sound can be diagnosed. Listening to combustion chamber, main bearing and valve is helpful to diagnose faults such as piston hitting cylinder head, excessive wear of cylinder shoulder, valve seat ring falling off, crankshaft fracture and main bearing loosening.
(6) the relationship between abnormal sound and other fault phenomena
When the engine has some abnormal noise fault, it is often accompanied by other faults. Therefore, these accompanying phenomena become an important basis for auxiliary diagnosis of abnormal sound.
To check the abnormal sound of the engine, it is necessary to have: manual intuitive method is a method to judge the technical condition and fault of the machine directly by looking, touching, trying and listening, or with the help of simple tools. Its characteristic is that it does not need special equipment, and the accuracy of diagnosis results depends on the technical level and practical experience of the diagnostician.
At first glance: observe the conditions of suspected failure mechanisms, assemblies and parts, such as the indicated values of various instruments, cracks and deformation of engine body, color of exhaust gas from muffler, oil dripping, water marks, etc., and then analyze and judge the working conditions of engine in combination with other relevant conditions.
The second touch: touch the temperature and vibration of the possible fault parts by hand, so as to judge the tightness of fit, the size of bearing clearance and the balance between parts and weight.
Three tests: all kinds of test methods are used to fully show the fault phenomena, such as pressing the horn, turning on the ignition switch or light switch, "cutting off" the spark plug, and rapidly increasing or decreasing the engine speed. If necessary, you can replace the good components or parts for comparative test.
Listening 4: It is to judge which is normal and which is abnormal according to the sound and sound law of different working conditions and parts of the engine. Such as whether there is knocking sound in the cylinder, whether there is shooting sound or "sudden, sudden" sound in the exhaust muffler, etc.
3.2 Diagnosis of Abnormal Engine Noise
3.2. 1 Diagnostic principle of abnormal sound
If the sound is slight and simple at low speed, growling at high speed or even smooth transition when accelerating or decelerating, it is normal sound. If the sound is accompanied by dull sound, crisp sound, short sound, subtle sound or strong sound, it means that the engine has abnormal abnormal noise. Whether it is serious or not can be judged according to the following conditions: if the sound only exists at idle speed, it will disappear automatically after speeding up, and the sound has not changed obviously during the whole use process, which belongs to harmless abnormal sound, and it is allowed to exist temporarily and be repaired at an appropriate time. If abnormal noise occurs during sudden acceleration or sudden deceleration, but the engine does not disappear during medium and high speed operation, and at the same time, it causes vehicle body jitter, so it is not allowed to continue to exist abnormal noise, and the reason should be found out immediately and eliminated. If the noise is sudden and severe during operation, the engine should not be used for continuous operation or audition diagnosis, but should be stopped immediately for inspection. Generally, the oil pan is removed first, and then the cylinder head is removed.
3.2.2 Diagnosis method of abnormal sound
To check the abnormal sound of the engine, it is necessary to have: manual intuitive method is a method to judge the technical condition and fault of the machine directly by looking, touching, trying and listening, or with the help of simple tools. Its characteristic is that it does not need special equipment, and the accuracy of diagnosis results depends on the technical level and practical experience of the diagnostician.
(1) Look: observe the conditions of the suspected faulty mechanism, assembly and parts, such as the indicated values of various instruments, cracks and deformation of the engine body, the color of the exhaust gas from the muffler, dripping oil stains and water stains, and then analyze and judge the working conditions of the engine in combination with other relevant conditions.
(2) Touch and test the temperature and vibration of the parts that may fail by hand to judge the tightness of the fit, the size of the bearing gap, the balance between the parts and the weight, etc.
(3) The test is to fully show the fault phenomenon by pressing the horn, turning on the ignition switch or light switch, and "cutting off" the spark plug, so as to quickly increase or decrease the engine speed. When necessary, components or parts can be replaced for comparative test.
(4) Listening is to judge which is normal and which is abnormal according to the sound and sound law of the engine in different working conditions and different parts. Such as whether there is knocking sound in the cylinder, whether there is shooting sound or "sudden, sudden" sound in the exhaust muffler, etc.
3.2.3 Diagnosis process of abnormal sound
According to the timing and duration of abnormal sound, abnormal sound generally exists at idle speed or low speed and high speed respectively. When abnormal sound occurs during idling or low-speed operation, diagnosis can be made in the following order:
(1) Check whether the abnormal sound is related to the cylinder position by the single-cylinder fire-breaking method. If the abnormal sound of the cylinder changes obviously after flameout, it means that the fault lies in the cylinder.
(2) If the abnormal sound of a cylinder does not change obviously after flameout, it means that the abnormal sound has nothing to do with the cylinder position. Check whether the abnormal sound is related to the working cycle and determine which mechanism is the fault.
(3) Then gradually increase the engine speed, listen to whether there is any change in abnormal sound, and judge the loss degree of the moving mechanism according to the change of abnormal sound with the speed.
④ In addition, in the process of diagnosis, attention should be paid to the influence of engine temperature change on abnormal sound.
When abnormal sound occurs during high-speed operation, diagnosis can be made in the following order:
① Gradually increase the engine speed from low speed to high speed. In this process, we should pay attention to the timing of abnormal sound.
(2) When abnormal noise occurs, let the engine run stably at this speed, listen carefully to the abnormal noise, and find out the cylinder position by single cylinder flameout method.
(3) If it is difficult to find out the cylinder position, listen to the abnormal sound distribution area.
(4) If there is no abnormal sound in the process of gradually increasing speed from low speed, but there is abnormal sound in the process of rapid acceleration or deceleration, the single cylinder fire extinguishing method and rapid change of speed can be used to determine which cylinder position the abnormal sound occurs.
Through the above diagnosis, we can basically find out the relationship between abnormal sound and engine load, working cycle, speed and temperature. If the abnormal sound conforms to some characteristics of abnormal sound, a diagnosis can be made. In addition, in the process of diagnosis, we should also listen to the vibration parts caused by abnormal sound and other accompanying fault phenomena, pay attention to the changes of oil pressure, oil filler and exhaust pipe, diagnose the fault, and draw a diagnosis conclusion.
Example analysis
I had a Jetta when I was an intern at FAW-Volkswagen. During use, the driver reported that Jetta's engine had abnormal noise. After on-site diagnosis, I found that:
① When listening to the engine outside, the abnormal sound is a short and firm "click, click" sound when idling; If the engine speed is from idle to medium speed, the abnormal sound is more clear, which is a kind of continuous knocking sound. With the increase of engine speed, the knocking sound is more prominent, and the abnormal sound is obvious when accelerating rapidly.
② No matter whether the engine temperature is high or low, the abnormal sound will not change.
(3) Keep the engine running at medium speed. When listening carefully, it is found that abnormal noise is a regular sound, and with the increase of engine speed, the frequency of abnormal noise increases.
(4) When the single-cylinder fire extinguishing method is used for inspection, the abnormal sound is weakened after the load of cylinder 3 is increased; After removing the load of other cylinders, the abnormal sound has no obvious change; After removing the load of cylinders 2, 3 and 3, 4, the abnormal sound attenuation degree is similar to that of cylinder 2.
⑤ Open the filler cap and listen to the sound. I found the abnormal sound crisp and loud.
⑥ When checking the abnormal sound, we observed that the oil pressure was low.
Through the above diagnosis and analysis, it can be seen that abnormal sound is related to engine speed, load and working cycle, but not to engine temperature; At the same time, the abnormal sound increases with the increase of rotating speed, and decreases after lifting the load of cylinder 3. Therefore, according to the characteristics of abnormal sound, it is preliminarily considered that the fault is caused by the looseness of the connecting rod bearing of cylinder 3. Combined with the abnormal sound position and low oil pressure, it is finally determined that the fault is the looseness of the connecting rod bearing of cylinder 3, which should be repaired immediately. After removing the connecting rod bearing bush, it is found that the bearing bush of cylinder 2 has been seriously peeled off, the surface has been slightly melted, and the bearing bushes of other cylinders are normal; After measurement, the size and roundness of the connecting rod journal on the crankshaft are within the required range. After replacing a pair of connecting rod bearings, the abnormal sound disappeared. Because the fault was found and dealt with early, the fault was prevented from expanding. At the same time, due to the analysis and diagnosis method of abnormal sound characteristics, the cause of the fault was correctly diagnosed, and the fault was eliminated in time.
4. Summary
The above is my initial understanding of Jetta through years of school study and internship at FAW-Volkswagen. Through the study at school, I know the principle of the car, where all the parts play a role, and the internship at FAW-Volkswagen gave me a good practical opportunity, so that I can apply what I learned from books to the real car. This paper introduces the components of Jetta. Through the study in FAW-Volkswagen, I know the common faults of Jetta, which makes me know more about Jetta, the strength of foreign automobile industry and why Jetta can sell well in China. I sincerely hope that our cars in China can go to the world one day earlier.
There may be some mistakes in what I have learned. I hope the teacher will guide me again, and I will keep trying to innovate in the future. Thank you very much for your teaching these years. I will keep that in mind.
[References]
[1] Li Peijun's Maintenance Manual of Jetta Two-Valve EFI Car, People's Communications Publishing House, June 2004, 5438+0.
[2] Wiki, Diagnosis and Analysis of Common Faults of Automotive EFI Engine, Press, Machinery Industry Press, 2008.
[3] Wiki "Fault Diagnosis and Analysis of Automotive EFI Engine", Machinery Industry Press, July 2008.
[4] Song Jingui, New Structure Maintenance of Imported Toyota Motor, Machinery Industry Press, 2000.
[5] How to repair abdominal muscles? Automobile ASR and SRS System-Automobile Maintenance Vocational Skills Training Series, Machinery Industry Press, 2005- 10, 1 version.