Failure diagnosis of BMW 535i after sudden flameout
  • Automotive

The crankshaft position sensor is an engine type N55B30A BMW F07 GT 535i sedan. The car was running normally in the city, when the engine suddenly felt the engine suddenly jitter and then flameout. When the engine was restarted, the starter turned normal, but the engine was unable to start, and the fuel tank showed the oil tank in the 1/2 oil level. At the same time, the instrument alarm showed: "abnormal fuel supply, engine power may drop, drive carefully! As soon as possible by the latest BMW after-sales service inspection. Fault analysis: ask the owner to know that 90% of the car is in the city road between the company and the home, there is an independent garage, refueling is at the designated regular gas station to add 97 gasoline. According to the failure phenomenon and maintenance experience, the fault can be preliminarily judged: (1) it may be the engine control system failure, such as DME damage caused by the failure of ignition, damage resulting in the DME received no signal, the injector can not open the fuel injection; (2) the most likely oil low voltage system fault. The basic components of the low pressure fuel system are CAS, DME, EKPS, gasoline pump and fuse. The system control principle is that CAS gives power to the EKPS control unit, DME communicates through PT-CAN2 and EKPS, EKPS gives power to the gasoline pump, and the gasoline pump work guarantee system has normal oil pressure. Therefore, the failure may be caused by the damage of the EKPS control unit, resulting in no power supply and inability to communicate, or damage to the fuse and gasoline pump. Fault diagnosis: connecting car charger for automobile computer diagnosis: detection of EKPS control unit without signal, diagnostic fault code CDC304: information (electric fuel pump state 335) missing, receiver DME (PT -CAN2), transmitter EKP (PT-CAN2); 481 B02: fuel pump control regulation current too high; 481B04: fuel pump control Regulation of current loss. T1612 STROO for fuel pump current check, install adapter interface box (631030) at EKPS line plug, measure EKPS No. 1 pin, no battery voltage when opening ignition switch, check EKPS wire and plug connection normal, check fuse fuse, reset 20A fuse, open ignition switch The measurement voltage is normal. It is considered that the trouble is removed and the engine is restarted, but it is still unable to start. A reexamination of the fuse was found again. Check the cause of fuse fuse, check the circuit diagram of the oil low pressure system, confirm that the pin 1 on the rear fuse bracket is in good condition with the line No. 1 on EKPS, confirming that the pin 2 on the EKPS is in good guidance. Check the control mode of EKPS control unit: the EKPS control unit is to ensure the fuel supply, and the engine sends 1 requirements information to the oil pump control system EKPS through the CAN bus. According to the fuel pump control mode, this information is described as a pulse width modulation regulation (pressure regulation), that is, by comparing the actual pressure in the supply line to the high pressure pump and the rated pressure, the engine will send 1 request signals to EKPS through the CAN bus. EKPS converts the request signal into a standard voltage. The standard voltage will be converted to pulse load parameter (pulse width modulation) and adjusted to this value with reference to the voltage actually added to the bus terminal KI.30. Through the above information analysis, the PT-CAN2 waveform is normal and the voltage is normal when the ignition switch is opened from DME to EKPS. Measure the 15WUP wake-up line on the EKPS plug pin 13 on the ignition switch to store the battery voltage. It can be determined that the control unit and the communication are normal. Therefore, the problem is most likely to appear on the electronic gasoline pump, the installation line plug adapter interface box (612350), the measurement of the electronic gasoline pump coil resistance is 0.646 omega (standard resistance about 2.8 omega), indicating that the electronic gasoline pump short circuit. In order to further confirm the cause of the short circuit of the gasoline pump, remove the electronic gasoline pump in the tank and check the contact of the electric line and plug of the electronic gasoline pump. In the disassembly of the gasoline tank and the electronic gasoline pump, there is no gasoline in the tank, which is different from the 1/2 oil level on the fuel tank. The gasoline pump and the gasoline float are not 1 integral components, the gasoline pump and the gasoline float are not the whole components. The gasoline float is installed on the built-in frame of the oil tank, and the gasoline float is carefully checked to be mechanical deformation. The float of the gasoline float is stuck on the top layer of the gasoline tank, causing the false display of the oil level; this is misleading to the driver and is suddenly in the course of driving. After the flameout, the engine is started many times, causing the internal overheating of the gasoline pump, which leads to the short circuit of the gasoline pump, the fuse fuse and the failure of the oil low pressure system to start the engine. Replace the electronic gasoline pump and gasoline float, install the fuse, check the deleted fault code with the computer diagnostic system, and show that the system is working normally. Test oil tank exhaust valve work normal, refueling to the gas gun jump gun, inspection instrument display as full tank of oil level, restart the car, the engine can run normally, troubleshooting. Summary and analysis: the fault surface is the damage of the electronic component gasoline pump, which causes the low pressure system of the fuel oil to work normally and the engine can not start normally, but the fault is actually due to the mechanical damage of the gasoline float inside the tank, and the fuel meter is wrong, which misleads the driver in the oil shortage situation. At the same time, the electronic gasoline pump caused by the frequent starting engine is overheated and burned, which further causes the failure of the oil low pressure system to work normally and the engine can not start normally.