Technical Paper on Electronic Control of Automobile Engine 1 Troubleshooting of Automobile Electronic Control Engine
This paper analyzes the causes of starting failure of automobile electronic control engine, and points out the methods of fault diagnosis and elimination.
Electronically controlled engine; Fault; Diagnosis; exclude
China Library Classification Number: F407 Document Identification Number: A
With the development of electronically controlled fuel injection technology and the continuous improvement of maintenance consciousness, in modern automobiles, when the automobile equipped with electronically controlled fuel injection engine is repaired, the electronic control unit (ECU) of the engine detects it by using a fault diagnosis instrument and carries out maintenance according to the fault code stored in the ECU. Most of them can identify the possible causes and locations of faults, which will bring great convenience to maintenance personnel.
Using data stream to diagnose the fault of electronically controlled engine, we must first lay a good theoretical foundation. With these theoretical foundations, when we are looking for faults, we will find the main source of the problems and analyze them. Then, we need to know the representation of the data of each sensor. Combined with the maintenance examples in actual maintenance work, talk about the application? Data stream? Experience in fault diagnosis of electronic control system.
1. Use? Static data flow? Analysis fault
Static data flow refers to the data of the engine electronic control system read by the scan tool when the ignition switch is turned on and the engine is not started. For example, the static data of the intake pressure sensor should be close to the standard atmospheric pressure (100-102 kpa); When the car is in a cold state, the static data of the coolant temperature sensor should be close to the ambient temperature. What are the following uses? Static data flow? Diagnostic example: Fault phenomenon: One morning after winter, a Jetta King car could not be started. Inspection and judgment: First of all, consultation was conducted, and the owner reported that it was difficult to start a few days ago in the morning, and sometimes it could be started after a long time, and everything was normal after starting.
It was repaired in another repair shop at first. The fuel pressure and cylinder pressure of the engine, fuel nozzle, valve timing, ignition timing and spark plug misfire have all been checked, and the problem has not been solved. Carefully re-examine the above items and found no problems. The engine was oily and caught fire, but it just wouldn't start. What is the reason?
Later, it was found that although the spark plug was started many times, it did not stop. Overflow? There are indications that the cause of the failure is insufficient cold start concentration. If the cold start concentration is not enough, what causes it? Is the coolant temperature sensor normal?
Check the engine ECU with a scan tool, and there is no fault code output. By reading the static data stream of the engine, it is found that the coolant temperature output by the engine ECU is 105℃, while the actual engine temperature is only 2-3℃. Obviously, the water temperature signal received by the engine ECU is wrong, indicating that there is something wrong with the coolant temperature sensor. For further confirmation, use a multimeter to measure the harness between the coolant temperature sensor and the computer. There was no open circuit or short circuit, and the 5V reference voltage given by the computer to the coolant temperature sensor was normal, so the coolant temperature sensor was replaced, and then started normally, and the fault was eliminated.
1. 1 direct observation method
Maintenance personnel rely on rich maintenance experience to ask the driver for detailed information, such as fault phenomena or symptoms, without using tools; Failure frequency; Whether it has been overhauled, and the external environment (climate, road conditions, engine conditions, etc.). ) when the fault occurs; When overhauling, start the engine, listen to the sound of the engine, carry out overhaul, judge whether there is air leakage, noise and other phenomena, and judge whether the parts in the overhaul part can work normally; Then, the basic items of the vehicle should be inspected to determine whether there is a fault reason, such as whether other parts of the vehicle are damaged, whether the connectors or connectors of the electrical circuit are loose, whether the wires of the system have traces of short circuit, wrong connection and burning, and whether there are pipeline breaks in the wiring. Reproduce the fault through trial operation to determine the cause of the fault.
Call fault code: know the inspected vehicle, master the data of the inspected vehicle and the accurate position of each component of the electronic control system. And the wiring diagram, wiring and test methods, including the use of test instruments; It is necessary to enter the self-diagnosis state according to the operating procedure required by the vehicle during operation, obtain the fault code in the system, quickly find the fault position according to the prompt, further detect and determine the fault existence point, and determine the consistency of the fault with the previous phenomenon, so as to judge and confirm the fault cause. Therefore, before retrieving the fault code, the vehicle engine should be inspected and the fault should be studied through basic inspection. Because different vehicle models have different inspection methods, conditions and steps, the vehicle maintenance data should be overhauled in strict accordance with the data requirements in the vehicle manual.
1.2 environmental simulation method
Because the fault of the engine electronic control system usually occurs in a specific environment, the electronic components in the electronic control system are sensitive to environmental changes, such as high temperature environment, violent bumping environment, rainy and snowy wet environment and so on. For the failure of environmental factors, three kinds of environmental simulation can be used for diagnosis. The first is the heating environment simulation method. Engine-based electronic control system is prone to failure when heated, such as some electronic components, wiring harnesses, sensors, actuators, etc. Because it is easy to fail when heated, it is necessary to simulate the environment. After the engine is started, it can be heated locally with a hair dryer. If there is a fault when heating an electronic component, it means that the component is related to the fault. Note: When heating, the temperature should not be higher than 60℃; When heating electronic components, it is not allowed to directly heat electronic components in ECU. The second is to use the humidification environment simulation method. When the fault of electronic control system occurs in rainy weather, humidification simulation method can be used to detect it to reproduce the high humidity environment.
2. use? Dynamic data flow? Analysis fault
Dynamic data flow refers to the data of the engine electronic control system read by the diagnostic instrument when the ignition switch is turned on and the engine is started. These data change with the engine working conditions, for example, the dynamic data of intake pressure sensor changes with the throttle opening; The signal of the oxygen sensor should constantly change between 0. 1-0.9V, and so on. By reading the dynamic data of the control unit, we can know the signal value sent by each sensor to ECU, and by comparing with the real value, we can quickly find out the accurate fault position.
2. 1 Method when there is a fault code
We can focus on the sensor data related to the fault code, analyze what causes the data change, and find out the cause of the fault.
Symptoms: The fuel consumption of a Santana 1.6i car (taxi) increased per 100 kilometers1L. Inspection and judgment: the owner reported that the spark plug was changed and the ignition timing was adjusted a few days ago, but the fuel consumption was still high. Communicate with the owner to confirm that it is not an oil problem. So connect the scanning tool and type? Engine system? , read the fault code as? Oxygen sensor signal out of tolerance? Is the oxygen sensor broken? Enter? Read the test data block? , read 16 channel? Oxygen sensor? The data of is displayed as 0.0 1V unchanged.
The oxygen sensor shows a value lower than 0.45V for a long time, which shows two points: one is that the mixture is lean, and the other is that the signal of the oxygen sensor itself has errors. Is the mixture lean? According to the dynamic performance of the engine, the mixture should not be lean, so the oxygen sensor is mainly inspected by artificially enriching the mixture (adding a few feet of oil) to observe the data change of the oxygen sensor. Through observation, when a few feet of oil is added, the data of oxygen sensor changes from? 0.0 1V？ A little change? 0.03V？ , that is, almost unchanged, further check whether the heating wire voltage of the oxygen sensor is normal, indicating that the oxygen sensor is damaged. Replace the oxygen sensor, and then read its data with a diagnostic instrument, showing that the change of 0. 1-0.9V is normal, and the maintenance process is over. The next day, the owner reported that the fuel consumption returned to normal and the fault was eliminated. This is a typical failure of high fuel consumption caused by the damage of oxygen sensor.
2.2 Fault-free code method
The fault location is determined by correlation analysis and quantitative correspondence analysis of basic sensor signal data.
Fault phenomenon: FAW Jiabao has a micro-surface, weak acceleration, accelerated tempering, and sometimes accelerated flameout. Inspection and judgment: it is preliminarily judged that the mixture is too thin. In order to prove this, I used two methods to verify it.
One method is to remove the air filter, inject carburetor cleaner into the air inlet, and carry out acceleration test at the same time. It is obvious that the acceleration is strong and does not backfire, and the fault phenomenon disappears, which can prove the judgment that the mixture is too lean. Another method is to connect the diagnostic instrument, read the fault code and display no fault code; Reading the data stream and observing the data of the oxygen sensor, it shows that it hovers around 0.3-0.4V. After adding several pedals, the data of the oxygen sensor immediately rises to 0.9V over 0.45V, and then hovers around 0.3-0.4V. This shows that the oxygen sensor is good, because it responds in time and changes normally after artificially adding rich mixture, which also proves that the mixture is really too thin. What causes the mixture to be too thin? Through analysis, the intake pressure sensor and fuel system oil pressure are mainly considered. First, judge the intake pressure sensor and enter? Read the data stream? Read the data of the intake pressure sensor, and it shows: static data 10 10mbar, atmospheric pressure, normal; It is 380mbar at idle speed, which is basically normal; In the process of rapid acceleration, the data can quickly rise above 950 millibar. These data and their changes indicate that the intake pressure sensor is basically normal. Next, check the oil pressure, but because the oil pressure gauge is broken, it is impossible to measure the oil pressure of the fuel system, so we have to replace the oil pump directly. After replacing the oil pump, the fault disappeared and the fault was eliminated. The final result shows that the fault is caused by the insufficient oil supply capacity of the oil pump, which leads to the lean mixture.
3. Concluding remarks
Use? Data stream? Fault analysis is convenient for maintenance personnel to know the comprehensive operation parameters of the automobile, and can quantitatively analyze the faults of the electronically controlled engine, and detect and replace related components in a targeted manner, so that many detours can be avoided in actual maintenance work, diagnosis time can be reduced, and work efficiency can be greatly improved.
References:
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[3] Liu Xiaoming. Common faults and maintenance of electronically controlled engine [J]. Heilongjiang land and resources, 20 1 1 (6): 5 1.
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