BMW engine fault yellow light on 2A80 fault code engine jitter.

Vehicle information: Vehicle model code: E7 1 Engine model: N55 Driving distance: 70 100KM Fault phenomenon: The owner reflects the yellow light of the vehicle engine and gives an alarm, while the vehicle engine shakes. Maintenance process: maintenance personnel confirm the fault: when the car is idling, there is engine jitter and the yellow warning light of the engine is on; The special computer for road test vehicle carries out high-speed test with normal power and reads the data stream. The engine computer (DME) has the following faults and related data flow: Analyze data flow. In general, the no-load intake of the N55 engine on BMW is 13( 15kg/h) when the idle speed is about 650 rpm. Compared with ordinary vehicles, the air intake measured by HFM is obviously lower than the actual situation. What is the reason for this? Through data flow detection, it is also observed that the throttle opening is only 2.37% under 50mbar vacuum, and it is about 4% under normal conditions. By reading and analyzing the detected engine data flow, it is considered that the fault is caused by air leakage behind the throttle. The possibility of leakage after throttle valve includes: fuel tank ventilation valve failure, intake manifold leakage, aging damage of throttle gasket, DME sealing problem, crankcase ventilation problem, engine block sealing problem, blocked fuel tank ventilation pipeline, DME showing signs of decomposition after HHE removed intake manifold and throttle valve (below), and six screws of DME and intake manifold showing signs of loosening, but the failure remains after reinstallation. Measure the crankcase pressure, which is close to the atmospheric pressure, indicating that the crankcase pressure is too high. The reasons for high crankcase pressure are: air leakage, poor or damaged cylinder head cover seal, poor or damaged crankcase seal, damaged crankcase ventilation device, and no adverse effect on vehicle acceleration during trial operation. Air leakage 2.3.4 What measures can be taken to isolate this fault? System principle. Test whether the engine cylinder leaks: According to the ventilation characteristics of the crankcase of N55 engine, it is found that the gas leaking into the engine block first passes through the crankcase ventilation valve, and then enters the air inlet through the small holes of the valve cover and cylinder cover. In order to prevent combustion and prevent these leaked gases from entering the cylinder, the diaphragm of the crankcase ventilation valve is pressurized. When pressure is applied, the diaphragm blocks the hole between the crankcase and the air inlet, so the gas in the crankcase will enter the cylinder. Through the above tests, it can be confirmed that there is 100% air leakage in the engine block, but the engine structure is complex, and the causes of air leakage may be valve cover, front and rear oil seals of crankshaft, sensor seal, etc. How to judge specifically? By observing whether the engine seal leaks oil, we can take the leaking seal as the key inspection object and pressurize the crankcase. It was found that the oil seal in front of the crankshaft was leaking oil. After replacing the crankshaft front oil seal, the air intake measured by HFM kept at 15kg/h, and the fault code was cleared. The test run is trouble-free, and the bus is trouble-free after half a year. Confirm troubleshooting. Maintenance summary: This fault maps some engine system faults of BMW, and air leakage has always been a common problem of BMW vehicles. However, the air leakage of the engine may be different according to different parts, and the engine failure and data flow performance may also be different. For the throttle opening of BMWN55 engine 2A80, compare the absolute pressure of intake pipe: overpressure fault definition: whether the throttle position is reliable according to the intake pressure. When the detected air quality exceeds the limit value, DME will recognize it as a fault. Therefore, several maintenance and inspection methods for this fault are summarized. Observe the data flow. Pre-throttle pressure, post-throttle pressure, throttle angle, pre-oxygen, post-oxygen, air flow, steady-state value (oxygen sensor data affects air flow. Values of two pressure sensors before and after throttle valve in flameout state. (Check the harness from DME to the rear throttle pressure sensor. Delete the adjustment value: Because the adjustment value can make up for the deviation of the mixture, observe the air flow after deleting the adjustment value. The car is hot, delete all the adjustment values and get on the bus. Before the deviation is filled, let's take a look at what is abnormal in the data flow, focusing on air flow and oxygen transmission voltage. After deleting the adjustment value, some faults can be eliminated. Are the oil seals and valve covers at the front and rear of the crankshaft leaking? Whether the filter of EPDW control valve is blocked or not, and whether there is any bad action. Isolation of tank ventilation: Unplug all pipes for tank ventilation from the throttle, plug the throttle hole, and try again to confirm whether the fault can be reproduced. Carry out cylinder pressure test to preliminarily judge the state of piston ring. Observe and clean the carbon deposit on the intake valve with an endoscope. Can solve most of the faulty vehicles. Check whether the three-way catalyst is blocked and clean it. Vt system deviation: replace the VANOS solenoid valve of normal vehicle. Observe the wear of the camshaft. Check the wear of the electronic valve mechanism and replace it. Cascade fault: When the throttle valve is too low or too high, BMW vehicles often have cascade faults. For example, after a fire, the pressure is reported to be too low, and after the mixture is diluted, the pressure is reported to be too high.