Symptom: a 2004 BMW E66760Li sedan, the user reflects the engine idling jitter, driving acceleration, the recent emergence of the engine after the start of the smell of gasoline.
    Troubleshooting: After receiving the car, the author first to the user to understand the car before and after the failure of any abnormal situation. Users reflect that some time ago because of the local typhoon causes, causing this car part of the water. At that time the water treatment did not appear after the failure, after a period of time there have been a variety of failures, but then most of them are repaired, only the engine failure has not been repaired. Cleaning the throttle in other repair shops, replacing the ignition coil and spark plugs did not solve the problem.
    This car is equipped with a N73 engine, which is a high-tech engine, 12 cylinders were V-shaped structure, 4 valves per cylinder, using the electronic valve full variable valve control technology (Valvetronic) and fuel direct injection technology.
    N73 engine fuel injection system, the injector nozzle is located in the combustion chamber, close to the intake valve, each cylinder of the injector installed in the same oil track. The oil cylinders of each column are supplied with high pressure fuel from a high pressure pump, which is driven by the exhaust camshaft. The high-pressure pump will pressurize the fuel from the electronic fuel pump, so that the fuel pressure increased to 5 ~ 12MPa, the compressed fuel through the high-pressure tubing to the oil rail, and then to the injector, fuel injector by the DME engine control unit according to the relevant sensor Signal to control. Because the fuel pressure after pressurization is very high, conventional fuel pressure gauges can not be used to measure the fuel pressure of high-pressure pipelines in general repair plants. And from the maintenance manual can be seen, the fuel injector control voltage between 85 ~ 100V, so the general car oscilloscope is difficult to use here to measure, fuel injection time can only use the fault diagnosis device to view.
    First, connect the original BMW Diagnostic Instrument GT1, select the menu in the 7 Series E65 project (because the GT1 menu does not provide E66 project, E66 and E65 only long axis models and short axis models of the points), fault diagnosis machine automatically identify the model Into the whole car electronic control system detection, detection of a lot of fault code, because it can not identify the true and false fault, so record the fault code after all cleared. This unit has two DME engine control units, DME-1 is 1 ~ 6 cylinder engine control unit, DME-2 is 7 ~ 12 cylinder engine control unit, in the query DME-1 fault code shows 2 cylinder bad The fault code, clear the fault code and then start again, the fault code again.
    The main data are as follows: air flow signal 15kg / h; oil rail pressure 3.0MPa; fuel injection time 1.89ms; accelerator pedal signal 1 is 0.72V, accelerator pedal signal 2 is 0.36V. Comparing with the standard data stream, it is found that the air flow signal is slightly larger and the fuel injection time is longer. Continue to view the data flow found the problem, 2 cylinder operation instability value has reached 5.10, while the other cylinder value is close to 0, indicating that 2 cylinder obviously poor work. The engine on the right side of the intake hose removed to see the 2-cylinder ignition coil is also affixed with a very new label, which shows just changed, for the sake of reliability, I also replaced a work of the normal ignition coil And the spark plug to test, the results of 2 cylinder still does not work (in this need to remind maintenance personnel attention, the author in the maintenance of BMW cars often encounter some repair shop new replacement of the ignition coil is bad). Continue to use the fault diagnosis instrument to detect the DME-2 engine control unit, which stores 8-cylinder bad fault code. It can be seen from the data stream that the unstable value of the 8-cylinder operation has reached 1.93, check the 8-cylinder ignition coil and Spark plug is just changed.
    Depending on the experience of maintenance, the cause of the overall engine failure may involve multiple systems, but the cause of one or more cylinders does not work. First, the fuel system is analyzed because the oil pressure shown on the fault diagnosis device is 3.0 MPa, which indicates that the pressure is normal and that the individual cylinder oil pressure should not be present. The injector is controlled by the engine control unit. The engine control unit The probability of the problem is very low. On the other hand, if there is a problem with the injector line of the individual cylinders, the system should store the fault code of the injector line short circuit or open circuit. As for the ignition system, the BMW car ignition system control line work is relatively stable, there is little problem, but the ignition coil and spark plugs sometimes problems, and the author with a test light to detect the 2-cylinder ignition line part, start the engine When the test light can flash, indicating that the ignition line is basically normal.
    The cylinder pressure should be checked next. If the vehicle does not remove the intake manifold, it can not measure the cylinder pressure, but the user is concerned that the maintenance personnel are not familiar with the structure of the engine and does not allow the intake manifold to be disassembled. I think of the user said that sometimes there is gasoline when the start, because the inspection has been removed when the fuel pipe, has a very heavy smell of gasoline, so decided to check the next day. The next morning, start the engine, there are some gasoline flavor, but look at the external tubing and did not find the place to leak, if there is leakage should be under the intake manifold tubing oil spill. Because the author of the N73 engine structure is very understanding, you can determine if you do not remove the intake manifold can not continue to check the fault, so convince the user to allow the demolition of the engine intake manifold. After removing the intake manifold, it was found that the fuel lines between the two rows of cylinders were partially oily but not severe. Why is the oil pressure leaked on the fault of the fuel pipe is still normal? I think it should be leaked very little, high pressure pump pressure compensation, so the data stream did not see the problem.
    Because there is an idle jitter fault in the engine before the user feels the smell of the car, so there should be other reasons for the idle jitter. Because only two cylinders work poorly, air flow meters, oxygen sensors and water temperature sensors and other components do not need to check, but should focus on checking whether there is leakage of the site and the cylinder pressure is normal.
    I then pay attention to a crankcase exhaust pipe is not inserted, which will lead to engine idle instability, this situation if you do not remove the intake manifold is not easy to find. Measure the pressure of the cylinders are normal, check the 2-cylinder and 8-cylinder intake manifold sealing, although the intake manifold bolts are tight, but from the manifold gasket traces can be seen with a slight leakage.
    Replace the leaky fuel pipe, install the exhaust gas circulation pipe, and replace the intake manifold gasket, start the engine, from the fault diagnosis device data flow can be seen in the normal value of the test found that the fault completely ruled out. In the later maintenance work, the author also found several cases because the intake manifold gasket leakage caused by the engine idling jitter BMW cars, including equipped with a N62 engine 745i sedan, hope that maintenance personnel attention.
    Summary: Although this car is due to several causes of failure caused by a number of fault phenomena, but directly lead to 2-cylinder and 8-cylinder poor work because the intake manifold gasket leak, if the fault appears in the common models, Should be easier to exclude. But for the use of a direct injection system of the engine, the former maintenance staff because they do not understand its working principle, not familiar with the specific structure of the N73 engine, so do not disassemble the inspection, also lost the opportunity to troubleshoot, while Causing the user to the maintenance staff do not trust. This case caused the author's thinking, I suggest that maintenance staff not only should pay attention to the vehicle electronic control system of learning, but also pay attention to the specific mechanical structure of the disassembly of the study, otherwise encountered a failure is easy to start the situation The