There is a Nissan Bluebird produced by 1995. The fault phenomenon is that the car has a slight impact after stepping on the accelerator when it is cold, and the idle speed is not good. After many inspections and maintenance, the problem still cannot be solved.
The car was originally repaired in the factory because it could not be started after washing the engine. After being dragged into the factory, water was found in the ignition system. After cleaning and drying, reinstall. Although the car has stopped, the idle speed is somewhat unstable. After inspection, it was found that the high-voltage line leaked electricity, and the distributor head and cover were also ablated. After obtaining the user's consent, the above components were replaced, and the engine failure was basically eliminated, but the user reported that the car was not easy to use and the throttle had a slight impact after the cold car was put into gear. Although the failure phenomenon is not obvious, the user insists on maintenance and claims that if the problem cannot be solved, the previous maintenance fee will be exempted.
When I received this car, it was a hot car. Because it is impossible to verify the fault phenomenon at the moment, we first analyzed it according to the situation described by the user, and thought that the fault might be in the oil circuit. Then, the exhaust gas was tested under no-load condition, and the test results were as follows: HC was 275ppm (standard value was 220ppm) and CO was 0.3% (standard value was1.2%) at idle speed; At high idle speed, HC is 120- 150 ppm, and CO is 0.3%-0.5% (there is only one dual-gas exhaust gas analyzer in our factory). Measure the cylinder pressure, and the cylinder pressure is normal. Carry out the cylinder power balance test, and all cylinders work normally. When the cylinder is broken, the HC and CO values of each cylinder change the same.
Can you find the problem from the above data? 7 of course. Although the two-gas exhaust gas analyzer itself has no function of data analysis and mixing specific concentration test (generally, the four-gas exhaust gas analyzer can directly see the mixing specific concentration through CO, O2 and excess air coefficient), it can be seen from the data that the exhaust emission of this car is low, which is too low for the car without oxygen sensor and three-way catalytic converter. Generally speaking, high CO COntent is due to rich mixing ratio, while low co content is mainly due to poor mixing ratio.
According to this idea, I will raise the exhaust gas of the car, adjust CO to 1.0, and adjust HC to 200ppm. When the car was completely cooled and tested again, the exhaust emission did not exceed the standard, and the original fault phenomenon completely disappeared.
The fault method of each system aims at comprehensively evaluating the combustion condition of the engine. The main contents of tail gas analysis include air-fuel ratio, ignition timing and conversion efficiency of catalytic converter. The main analysis parameters include the contents of CO, HC, CO2 and O2, and air-fuel ratio (A/F) or excess air coefficient. See table 1 for tail gas analysis items.
Second, the basic rules of tail gas analysis
The readings of HC and O2 are high, which is due to the fire caused by poor ignition system or too thin mixture. When the measured values of CO and HC are high, but the values of CO2 and O2 are low, it indicates that the engine working mixture is very rich. If there is not enough oxygen in the combustion chamber to ensure normal combustion, the reading of CO2 is usually opposite to that of CO. The more complete combustion is, the higher the reading of CO2 is, and the maximum value is between 13.5% and 14.8%. At this point, the reading of CO should be equal to or close to 0. O2, which is one of the most useful diagnostic data. The reading of 02, together with the other three readings, helps to find out the difficulties of fault diagnosis.
Usually, the O2 reading of a car equipped with a catalytic converter should be 1.0%-2.0%, indicating that the engine burns well and only a small amount of unburned O2 is discharged through the cylinder. If the reading of 02 is less than 1.0%, the mixture is too rich, which is not conducive to combustion. If O2 reading exceeds 2%, the mixture is too lean.
Using the power balance test (according to the manufacturer's instructions) and the reading of the four-gas exhaust gas analyzer, we can see the working conditions of each cylinder. If the readings of C0 and CO2 in each cylinder drop, while the readings of HC and CO2 rise, and the rising and falling amounts are the same, it is proved that each cylinder works normally. If only one cylinder has a small change, the other cylinders are the same, indicating that the ignition or combustion of this cylinder is abnormal.
In the adjusted closed-loop electronically controlled automobile exhaust, the HC content is about 55~ 100ppm, the CO should be less than 0.5%, the O2 is 1.0% ~ 2.0%, and the CO2 is 13.8% ~ 15.0%.
See Table 2 for the detection value of automobile exhaust and the judgment and analysis of system failure.
Three, several common gas analyzer
There are many kinds of automobile exhaust gas analyzer, including two-gas, four-gas and five-gas, which are introduced respectively below.
Double gas exhaust gas analyzer
Dual-gas exhaust gas analyzer is used to measure the volume fraction of C0 and HC in automobile exhaust. However, if the automobile exhaust pipe or the measuring pipeline in exhaust gas analyzer leaks, the exhaust gas diluted by the outside air will be detected, and the measured values of C0 and HC will decrease, which naturally cannot reflect the true content of the exhaust gas. At present, most of the dual-gas exhaust gas analyzer used in China do not have the function of checking its own leakage, so even if the dual-gas exhaust gas analyzer is used to measure the automobile exhaust, it cannot truly reflect the engine failure.
2. Four gas exhaust gas analyzer
With the increase of vehicles equipped with three-way catalytic converters and electronic control systems, the emission standards of vehicles are becoming more and more stringent, so it is necessary to measure the exhaust gas more accurately and diagnose the causes of vehicle emissions exceeding the standard. Four-gas exhaust gas analyzer not only has all the functions of two-gas exhaust gas analyzer, but also can diagnose and analyze faults. Besides C0 and HC, it can also measure CO2 and O2, engine oil temperature and speed, and calculate excess air coefficient and air-fuel ratio A/F, etc. Therefore, the four-gas exhaust gas analyzer can be used not only as an environmental protection detection instrument, but also as a diagnostic tool for engine fault detection and analysis.
We have explained the analysis of several kinds of exhaust gases before, and here we only briefly explain the coefficient of air passing through stars. The passing air coefficient can tell us the air-fuel ratio intuitively. In theory, the over-the-star air coefficient of the mixture = 1 is the most standard, but it can't be constant in practice, so it is generally designed to be 0.97- 1.04 (some cars have specific instructions), which is also an ideal collocation. If it is greater than this value, it means that the air-fuel ratio is too large and the mixture is too lean; If it is less than this value, it means that the air-fuel ratio is too small and the mixture is too rich.
The four-gas exhaust gas analyzer can also provide engine speed (RPM) and engine temperature (temp) as reference data for fault diagnosis.
Five gas exhaust gas analyzer
When C0 and HC decrease, the concentration of NOx in exhaust gas may increase. In order to monitor the concentration of NOx, a five-gas exhaust gas analyzer must be used. Moreover, N0x is often produced under high temperature and heavy load. If there is no chassis dynamometer, it can only be measured by road test.
Fourth, several application examples
A Jetta car equipped with ATK's new 2-valve engine and three-way catalytic converter. Users reported that the engine of the car was unstable and the measured exhaust emissions exceeded the standard seriously.
Jetta's brand-new 2-valve ATK engine adopts an electronically controlled multi-point sequential fuel injection management system, which is a closed-loop centralized control system integrating fuel injection, ignition, idling, detonation, air conditioning, self-diagnosis and home returning.
According to the fault phenomenon of the car, the spark plug was first checked and it was found that the spark plug gap was too large. After replacing the new parts, the exhaust emission situation has improved slightly, but the improvement is not obvious. Connect the scan tool V.A.G 1552, test the engine electronic control system, and call out the 1 fault code (oxygen sensor). According to the prompt of fault code, check the harness connecting oxygen sensor and engine computer. No short circuit or open circuit was found, so replace the oxygen sensor. After the test run, the exhaust gas was continuously measured, and the exhaust emission index was still high, but the engine electronic control system showed no fault.
Measure the pressure of injection system with fuel pressure gauge. When the engine is idling, the oil pressure is 250kPa, 300kPa when it accelerates rapidly. After turning off the ignition switch 10 minutes, the system keeps the pressure at 200kPa, and the above data are normal. Next, the nozzle was removed for ultrasonic cleaning, and its resistance was15Ω, which also met the standard. Connect the press, observe that the atomization state of the nozzle is good, and check that there is no short circuit or open circuit in the connecting harness of the nozzle.
Continue to check the ignition system, and measure the resistance of ignition coil and high voltage line with multimeter. The engine was tested after recovery, and the fault still existed. Search the fault memory with V.A.G 1552, and there is still no fault code. When reading the measured data, it is normal to observe that the signal voltage of the oxygen sensor changes between 0.2-0.8V. The data of the intake pressure sensor also meets the standard. So it is suspected that there is something wrong with the three-way catalytic converter. After the replacement, it was put into trial operation, and the exhaust emission still exceeded the standard. Check whether the valve timing and timing mark are correct; It is suspected that there is something wrong with the quality of gasoline. After cleaning the oil tank and pipeline and replacing high-quality gasoline, the situation has not improved at all.
Careful observation shows that if the engine runs at idle speed without a road test after starting, the exhaust emission is basically qualified; The road test is about 2km, and the exhaust emission index rises; If the interval between each start is more than 30 minutes, the idle speed measurement is basically qualified. According to the above situation, I decided to replace the engine computer, but replacing the computer didn't help.
Is there anything wrong with other parts? So with the idea of giving it a try, the exhaust manifold was removed for inspection. Compared with the new exhaust manifold, it was found that the exhaust sampling hole of the automobile oxygen sensor was smaller. When the new exhaust manifold is used for exhaust gas detection, all indicators will be significantly reduced. After the road test, the exhaust emission is still qualified. Restore other parts replaced by the car and continue the test run. The exhaust emission has never exceeded the standard.
It can be concluded that the fault location is in the exhaust sampling hole of the oxygen sensor. Because the exhaust gas discharged from the cylinder is in a high-speed flow state, it forms a vortex when it travels to the sampling hole of the oxygen sensor, which causes the exhaust gas not to be updated in time here, which makes the oxygen sensor unable to accurately feed back the synchronization signal to the engine computer, which leads to the failure of the engine computer to correct the fuel injection pulse width according to the actual working conditions, and finally leads to the failure that the engine works abnormally and the exhaust emission exceeds the standard seriously.
There have been such failures in a number of vehicles, all because the sampling hole of the oxygen sensor was not properly drilled after the exhaust gas transformation, which led to the oxygen sensor being unable to effectively collect the exhaust gas, resulting in inaccurate signals.
A Toyota Camry with 5S-Fe engine has unstable idle speed and often shuts down.
The car adopts the electronic control system of TCCS engine. First, the fault code is called, and the engine fault indicator light on the instrument panel is displayed as a normal code. Four-gas exhaust gas analyzer is used for testing, and the test results displayed by the instrument are shown in Table 3. It can be seen from the test results that HC and O2 are both very high, which is an important feature of the imbalance of air-fuel ratio. The value of C0 is low, while CO2 is at the peak, indicating that the combustible mixture has been completely burned, and there should be no problem with the ignition system. The entry value is high. Comprehensive analysis shows that the engine mixture is lean, so the fault inspection should be carried out from the intake system and oil supply system.
Test vehicle: no air leakage and wrong vacuum tube insertion; The PCV valve is well sealed and the oil dipstick socket is in good condition. Start the engine and spray carburetor cleaner around the intake pipe gasket and EGR valve. It is found that the idle speed tends to be stable with the increase of rotating speed. When the EGR valve is removed, it is found that there is a small amount of carbon deposit around the needle valve and a large amount of carbon deposit on the EGR valve channel. The needle valve can't fall into the valve seat, which causes the mixture in the intake manifold to be diluted by exhaust gas, thus the idle speed is unstable and the engine is easy to stall.
Clean the EGR valve thoroughly, put on a new gasket and start the engine, and everything will return to normal. The exhaust gas analyzer is used again for testing, and the results are shown in Table 4. All data are within the standard range, troubleshooting.
From this example of fault diagnosis, it can be seen that after the necessary routine inspection of the faulty vehicle is completed, the essential cause of the fault can be quickly found by using the exhaust gas analyzer, and the maintenance scope can be narrowed.
A Guangdong Samsung 65 10 vehicle, equipped with 97 Chrysler Dodge 3.3L engines, has a mileage of140,000 km.
Fault symptoms: when the light throttle is engaged to 1200 r/min, it sometimes turns off, and when it is not turned off, the idle speed drops to 400-500 r/min or even lower; There is no fault in the emergency refueling door, which is easy to start after flameout.
Fault analysis: during the trial operation, there is no obvious feeling of oil cut-off and fire cut-off, but there is always a feeling that the air intake is not enough. After inspection, there is no fault in the idle system, and the idle motor has been replaced in other repair shops, and there is no problem; The throttle body has also been changed, no problem; Using additional air intake (disconnecting the vacuum tube behind the throttle body) can't solve any problems. No matter how it is tested, there are no signs of failure, and the engine speed drops from 1200 r/min to 800 r/min very smoothly. It is suspected that there is something wrong with the intake pressure sensor. It may be that the throttle slows down and the intake air volume cannot be well sensed. Therefore, the data flow function of the detector is used to observe all the data in real time, and no wrong data flow is found, and the MAP value is normal. After careful inspection and measurement of the oil supply system and ignition system, no fault was found.
Up to now, it should be said that I only feel a little fault clue from experience, that is, I feel as if the air intake is too small. Because it is suspected that the fault is caused by too little intake air, some clues can be found through exhaust gas detection, so the exhaust gas is measured, and the test results at idle speed are shown in Table 5.
According to the measurement results, we can find that the mixture is lean (more than 1.03) and the combustion is good (CO2 is high, close to 15%). Through the above analysis, it can be indirectly proved that there is a fault in the air intake or oil supply system of the automobile. In order to test this analysis, all the components that affect the intake air volume or the perceived intake air volume are listed one by one, and the faulty components are determined through step-by-step analysis and elimination. These components are: idle motor, throttle body and its sensor, MAP sensor and EGR valve. The first few components have been inspected and tested. At present, only the EGR valve has not been inspected.
The function of EGR exhaust gas recirculation valve is to introduce a part of exhaust gas into the inhaled fresh air (or mixed gas) and return it to the cylinder for recirculation to reduce NOx emission. Because N0x is mainly generated under high temperature and oxygen-enriched conditions, the exhaust gas is inert gas, which absorbs heat during combustion, which will reduce the maximum combustion temperature and reduce the amount of N0x generated. However, excessive exhaust gas recirculation will affect the normal operation of the engine, especially at idle speed, low speed and low load, and when the engine is running in cold state, the exhaust gas involved in recirculation will obviously reduce the performance of the engine. Therefore, the amount of waste gas involved in recovery should be automatically adjusted according to the working condition and the change of working condition. According to the different engine structures, the exhaust quantity entering the intake manifold is generally controlled between 6%- 13%.
In the EGR system, the exhaust manifold communicates with the intake manifold through a special channel, and an EGR valve is installed on the channel. The amount of exhaust gas participating in recirculation is controlled by controlling the opening of the EGR valve (as shown in Figure 1). The opening or closing of EGR valve is controlled by the vacuum degree of vacuum chamber above the valve, and the vacuum degree is controlled by EGR vacuum solenoid valve controlled by ECU.
The EGR solenoid valve is controlled by ECU, which controls the duration of the electrification of the EGR solenoid valve according to the engine speed, air flow, intake pipe pressure, temperature and other signals, so as to control the vacuum degree above the vacuum chamber of the EGR valve, thereby controlling the opening of the EGR valve and changing the amount of exhaust gas participating in recirculation.
In the EGR exhaust gas recirculation system equipped with back pressure correction valve, the back pressure correction valve is installed in the vacuum pipeline between EGR (vacuum) solenoid valve and EGR valve, and its function is to additionally control the monthly F gas recirculation according to the back pressure in the exhaust manifold. That is, when the engine is in a light load state and the exhaust back pressure is low, the back pressure correction valve keeps the EGR valve closed and no longer circulates the exhaust gas; The back pressure correction valve allows the EGR valve to open for exhaust gas recirculation only when the engine load increases and the back pressure of the exhaust manifold increases.
The back pressure of the exhaust manifold acts under the back pressure air chamber of the back pressure correction valve through the pipeline. When the engine is under light load and the exhaust back pressure is low, the diaphragm of the air chamber moves downward under the action of the valve spring, so that the correction valve closes the vacuum channel. At this time, the EGR valve is kept closed by its valve spring, so exhaust gas recirculation is not carried out. When the engine load increases and the back pressure of the exhaust manifold increases, the back pressure below the back pressure air chamber of the correction valve increases, the diaphragm moves upward against the elastic force of the valve spring, the correction valve opens, the vacuum controlled by the EGR solenoid valve enters the vacuum air chamber above the EGR valve through the back pressure correction valve, the EGR valve is sucked open, the monthly F gas recirculation channel is opened, and the exhaust gas is recovered.
The EGR solenoid valve is controlled by the ECU of IJ. ECU controls the degree of vacuum entering the EGR valve by controlling the opening of the EGR solenoid valve according to the rotation speed signal, intake pressure signal, water temperature signal and air flow signal, so as to control the opening of the EGR valve and change the amount of exhaust gas participating in recirculation.
Through the above analysis of the working principle of EGR valve, we can know that EGR does not participate in the work at idle speed and light load, otherwise some tail gas will enter the combustion chamber, which will not only reduce the temperature of the combustion chamber, but also worsen the combustion environment and hinder the entry of fresh air.
Troubleshooting: Replace the EGR valve, and the fault will disappear completely.
An Audi A6 car, equipped with a 2.8LJV6 electronically controlled engine, has slight jitter at idle speed and slow acceleration.
Fault inspection: The detected ignition waveform is basically normal, but slightly unstable. Measured tail gas, C0 is 0.3%-0.5%, HC is 200-500ppm, fluctuating within this range. Check with V.A.G.1552 detector, and no fault code is output. The data flows through the fault detector V-Man .G 1552, and the working parameters of the engine electronic control system are normal.
Analysis of test results: according to the customer's inquiry and the symptoms of slow acceleration, we should consider cleaning the injector; The C0 value is normal. Although the HC value meets the pollutant emission limit standard, the vehicle is equipped with an oxygen sensor and a catalytic converter, and its C0 value should be lower than 0.5% and HC should be lower than 100 ppm. The test results show that the HC value of the vehicle is higher than this, which is standard and fluctuating, and it is abnormal from the factory standard. Therefore, considering that the engine may catch fire, it is necessary to further check whether the ignition system has a slight open circuit or short circuit fault, especially a short circuit fault.
Troubleshooting: Clean the fuel injectors, and observe the atomization of fuel injectors in each cylinder and the uniformity of meteors, all of which are good. After checking the ignition system, it was found that there was a slight short circuit (leakage) in the high-voltage line of one cylinder, so the high-voltage line was replaced. Because the spark plug gap was too large, it was also replaced. Engine jitter has been improved slightly, but it has not been completely eliminated. The HC value of tail gas detection has not decreased much, and it still fluctuates. It is considered that the fault may still be caused by fire.
In order to further diagnose the fault, the exhaust gas detection ports (usually sealed with bolts) next to the oxygen sensor of the left and right F-gas manifolds were tested respectively. The results show that the C0 value of the exhaust gas discharged from the left cylinder is about 0.5%, and the HC value is about 125ppm (which is slightly higher than that measured in the F manifold because it is measured before the catalytic converter), and the fluctuation is very small. The value of C0 in the exhaust gas discharged from the right cylinder is also about 0.5%, but the value of HC fluctuates from time to time between 125-250 ppm. So the problem should be in the right cylinder. Therefore, the high-voltage line and spark plug of the right cylinder were inspected, and it was found that one of the three electrodes of the spark plug of the second cylinder was too small. After adjustment, it was reinstalled, and the fault was completely eliminated. The exhaust gas detection value also met the factory standard.
At present, more and more vehicles are equipped with catalytic converters, and it is sometimes difficult to measure exhaust gas. When the fault can't be well analyzed, we can try to measure it before the catalytic converter, which may reflect the engine emissions more truly. At the same time, it is necessary to compare the measurement results before and after the catalytic converter to judge whether the conversion efficiency of the catalytic converter is normal.
A Mercedes-Benz S320 car, the engine idling is unstable, and the jitter is serious, but the acceleration is normal.
Fault detection: call the fault code of the vehicle and display it as normal code; The secondary waveform of ignition was tested by oscilloscope, and the result was normal. Test the cylinder pressure of each cylinder, which is within the standard range; The air intake and vacuum system shall not leak; Four-gas exhaust gas analyzer was used to detect the exhaust gas, and it was found that the data was very unstable at idle speed. The data of 1 group are shown in Table 6, and the detection values of the four gases are all high. Test again. See Table 7 for the data.
Analysis of test results: By comparing the above test results, it is found that HC and Co always increase or decrease at the same time, CO2 fluctuates, the combustion efficiency is unstable, O2 cannot fully participate in the reaction, and the value is always high. Therefore, it can be judged that the formation of mixed gas and the combustion environment are very bad. It is speculated that the injector is blocked, which leads to the seal between the injector needle valve and the valve seat. The fuel injectors of each cylinder do not inject fuel or inject less fuel when it is injected, and continue to inject fuel when it is not needed, resulting in abnormal oil supply and extremely unstable detection data of four gases.
Troubleshooting: Do the fuel injection pulse width test and idle for 3.5ms, which is within the normal range. Remove the fuel injectors for each cylinder and check them. Sure enough, each injector has a different degree of blockage. After thorough cleaning, put on the second interview car and everything returned to normal.
From the maintenance process of the fault, it can be seen that in the inspection of the fuel system, some maintenance links can be omitted by using the exhaust gas analyzer, such as the test of oil pressure, the detection of fuel pump, oil pressure regulator and fuel filter. From another point of view, if the exhaust gas analyzer is used to test before the relevant inspection in emergency repair, the fault point may be found at the beginning of diagnosis.
An Audi 100 car, equipped with a 2.6LV6 electronically controlled engine, has severe vibration and weak acceleration during driving, and the smell of gasoline from the exhaust pipe is choking.
Fault detection: The electronic control system of the engine is detected by V.A.G 1552 microcomputer fault detector, and there is a fault code, indicating that "the adaptive correction of right fuel has reached the limit". Using V.A.G 1552 microcomputer fault diagnosis instrument to detect the data flow of engine electronic control system. It is found that the fuel correction coefficient on the left and right sides is too large, which is -3.8%-0% on the left and 10%- 12.9% on the right. Check the ignition system with the engine comprehensive analyzer and analyze the cylinder pressure. It is found that the breakdown voltage of the ignition waveform of the third cylinder is low, and the cylinder pressure is low (too large cylinder pressure difference will also lead to engine jitter). The tail gas is detected by exhaust gas analyzer, and the Co is 0.9%- 1.3%, while the HC is as high as 2,800-2,900 ppmo.
Analysis of test results: According to the test results, it can be considered that the mixture on the right side is too lean, and the control computer keeps enriching the fuel system on the right side, which has reached the correction limit. In order to judge whether this result is caused by the signal of the right oxygen sensor, the signals of the left and right oxygen sensors and their response to the change of air-fuel ratio, and the response ability of the electronic control unit to the change of the signal of the oxygen sensor are tested first. Therefore, the mixture was artificially made too rich and too lean, and it was found that the oxygen sensor and the electronic control unit were functioning normally, which could be considered as a fault caused by reasons other than the control system.
According to the above test results, the ignition waveform is basically normal, so it can be considered that the ignition system is normal, but too high HC indicates a fire, so it can be considered that the fire is probably caused by the mixture being too thin and exceeding the ignition limit. However, judging from the Co value in the tail gas, the actual mixture is not too thin, so it is likely to be a fault caused by air leakage in the intake system. By measuring the cylinder pressure, it is found that the pressure of the third cylinder is about 100kPao lower than that of other cylinders.
Troubleshooting: When disassembling the intake manifold, it is found that the actual compression surface width of the intake manifold gasket is only about 1mm (at least 4-5 mm). The reason is that the mounting surface of the intake manifold is V-shaped. After installing the gasket, when installing the intake manifold again, the gasket slipped down carelessly, which reduced the sealing band and caused serious air leakage. Even if the fuel correction reaches the limit, it cannot be fully compensated. After thoroughly eliminating the above fault points, test run and eliminate the fault.
A Buick G car in Shanghai, the fault symptom is that the engine exhaust emits black smoke.
Diagnosis and elimination: After the engine was overhauled, everything was normal at first, but there was a slight air leakage in the exhaust pipe connecting pad. After continuous trial operation, it is found that the engine has unstable idle speed and poor acceleration, and the fault light lights up and gives an alarm. Upon inspection, the fault code is four 13 1, that is, the oxygen sensor is faulty. When the engine is warm-started, it will be measured (without pulling off the bracket). The voltage of the oxygen sensor is 0.28 V, and there is no change. After replacing an oxygen sensor, the engine was fine at first, but after running for a period of time, the fault appeared again, the idle speed was unstable, and the exhaust pipe smoked black smoke. After removing the spark plug for inspection, carbon deposit was found. After changing a new set of spark plugs, it ran for about half an hour, and the idle speed was unstable. The spark plug was burnt out by carbon deposit. At this time, the fault light is on again, and the inspection shows the fault code P0 17 1, that is, the mixture is too thin.
The repairman thinks that the fault is not in the oxygen sensor, because the fault is aggravated rather than improved after replacing the oxygen sensor. After measurement, the oil pressure is normal, and seven sensors, such as air meteor, water temperature and throttle position, have been checked, but the fault has never been ruled out, so I went back to check the new oxygen sensor. After on-board measurement, the voltage of the oxygen sensor is about 0. 18V, which is the same as the data found by the detector, which proves that the detector can completely receive the voltage of the oxygen sensor. Disconnect oxygen sensor and measure PCM terminal wiring. The voltage is only 0.32 V (theoretical value is 0.45 V), and it is suspected that the circuit is faulty or the PCM is damaged.
Using the exhaust gas analyzer to check the exhaust gas, it is found that the C0 content is close to 4% and HC reaches about 300ppm at idle speed. Through tail gas analysis, it can be considered that the mixture is not too rich at this time. When measuring the oxygen sensor on the train, the voltage is still very low (this phenomenon can be explained as the mixture is too thin). Disconnect the oxygen sensor, and measure the terminal voltage of PCM with a digital multimeter to be 0.44 V, indicating that the basic conditions of the line and PCM are normal. Why are there two completely different explanations? 7. Is there something wrong with the new oxygen sensor? Therefore, the simulator is used to simulate the function of oxygen sensor values.
Connect the green oxygen sensor dedicated line and black connecting line of the simulator to the output circuit of the oxygen sensor on the vehicle;
Set the intermediate function selector switch to knock /0xy position;
Set the right function selection switch to VoHs/0xy position;
Start the engine, and then open the SST disk. At this time, SST dish 4 sends out a constant continuous signal of 0. 15V, which simulates the signal sent by the oxygen sensor in the state of lean mixture.
Press the "0(y)" key above the simulator, and the simulator will generate a constant continuous signal of 0.85 V to simulate the signal from the oxygen sensor in the state of rich gas mixture;
After simulating seven oxygen sensors with the simulator, the detector reads the data stream and finds that the input signals of the oxygen sensors also change together.
When the simulator voltage is 0.85 V for a long time, the observed CO value of exhaust gas drops to 0.65%, which shows that PCM controls the system well and the fault is still caused by oxygen sensor. The oxygen sensor was installed on other vehicles for testing, and no fault was found. Data flow, combustion, exhaust and driving are all normal.
Through the above experiments, it can be proved that there is almost no fault in the system, and the reason for the problem lies in the oxygen sensor signal. Because there is air leakage in this car, will it be because the exhaust bag leaks, resulting in negative pressure in the exhaust bag, leading to the introduction of external vacuum into the exhaust system? 7. After checking the ldF gas system for air leakage, try to repair the exhaust pipe and troubleshoot.