Deep understanding of the works to quickly resolve difficult problems

Symptom: a 2009 BMW F02 740Li annual car, type N54 arranged inline 6-cylinder turbocharged engine and a high-precision injection, mileage 21,000 km. According to reflect the user, when the vehicle is traveling in a rapid acceleration meter engine failure warning light, ldquo Central Information Display (CID) occurs; the decreased engine power rdquo; tips, when rapid acceleration feeling weak, slightly slower acceleration feel no effect, the engine is operating normally, there is no obvious jitter at idle.

Check Analysis: N54 turbo type engine system uses a dual turbocharger failure for ease of understanding, it is necessary to related components and operation of dual turbocharger system will be briefly described ( figure 1).


(1) an exhaust gas turbocharger function is to improve the intake air amount of the engine combustion chamber, and the response of the turbocharger speed is very important for the engine, the driver is not allowed to request (i.e., accelerator pedal position) to make a delayed response, i.e. so that the driver can not feel ldquo; turbo lag effect rdquo ;, so using two engine on N54 the small-sized turbocharger in parallel to solve this problem. An exhaust cylinder 2 and 3 drive the exhaust gas turbocharger (22), by a cylinder of the cylinder row 2, 5 and 6 of the exhaust gas drives the exhaust gas turbocharger (1) by the banks. The reason why a small turbocharger acceleration process has the advantage that the moment of inertia of the turbine is small, the boost pressure can reach a higher and faster.

supercharging pressure (2) of the turbocharger with engine speed and load reaches the exhaust gas flow rate at the turbine is directly related to, and dependent on the flow rate and the speed of the airflow. The engine management system regulated by the wastegate valve (3 and 21) supercharging pressure, wastegate valve operated by a vacuum actuator (20 and 19), the actuators by the electronic engine management system via pneumatic pressure transducer EPDW (4) when controlled, can be delivered through all or part of the wastegate at the turbine exhaust gas stream to achieve the required boost pressure, the wastegate valve begins to open, the discharge part of the airflow through the bypass passage, which prevents the turbocharger ‘s speed continues to rise, in order to meet requirements of different engine operating conditions. E.gWhen the engine is in the idling condition, the exhaust bypass valve of a turbocharger 2 are closed, so that the entire exhaust gas flow can at this stage at low engine speeds for the acceleration of the compressor. N54 engine load is achieved by controlling the throttle valve and the wastegate valve, in all operating conditions, the waste gate valve of the engine are involved in the load control curve in accordance with the process characteristics.

(3) a turbocharger pressure control on the following parameters: inlet air temperature, engine speed, throttle position and atmospheric pressure. The engine control unit controls the electro-pneumatic pressure transducer EPDW these parameters can be checked by the control result achieved supercharging pressure (throttle pressure before the measurement). The data is then reached a predetermined supercharging pressure is compared with the characteristic curve can be corrected according to the comparison result of the control parameters when necessary, so the system itself always be controlled and monitored during operation. If the design of the engine boost pressure of the turbocharger is running above the permissible limit, may result in the engine operating temperature is too high. If a malfunction occurs during operation, or untrusted value associated with modulation turbocharger sensor failure, the control of the wastegate valve is cut off, the valve is fully open and therefore will not be pressurized by the indicator and CID EML prompt the driver information display.

on the face to understand the working process of twin turbochargers, will analyze the fault of the car helps a lot. Connection failure diagnostic ICOM, DME fault memory system is read by ISID ldquo; 30FE DME exhaust-gas turbocharger, the boost pressure is too high; 3100 DME boost pressure control Close rdquo ;. ISID detection program according gradually check, it is determined that the analysis result of two electro-pneumatic pressure transducer while EPDW fault, i.e. integral with the electro-pneumatic pressure transducer 2 boost pressure regulating solenoid valve (FIG. 2) is faulty. Remove the two solenoid valves, a solenoid valve measured by a multimeter, found a few ohms, and no open circuit. Connect the conduction of the solenoid valve is energized, check the vacuum tube, and turned off normal. A solenoid valve then found above a small square plastic cover, the internal opening screen, can see the filter is covered with dust.

FIG. 2

will cause the clogging of the filter is soBarrier it? Reanalysis uses boost pressure control solenoid valve, its role is to control the access to the vacuum pressure wastegate actuator. From the above description, in all operating conditions, the waste gate valve of the engine load are involved in the control process according to the curve characteristic specific to the control solenoid valve regulated by the supercharging pressure, the solenoid valve which requires fast response DME instructions, the need to change the vacuum pressure line. If the solenoid valve control phase from a larger to a smaller pressure required conversion stage pressure control, by means of atmospheric pressure outside it is necessary to help pressure rapidly, in order to achieve fast response to the wastegate valve actuator adjusted to change the turbine object of the supercharging pressure. And the electromagnetic relief valve hole is external filter port, if the port clogged filter, it will directly affect the speed control solenoid valve wastegate valve actuator, would result in engine intake pressure is higher than the actual needs, That boost pressure is too high. DME is detected by the charge air pressure and temperature sensors (12) to the pressure is too high, it will wastegate control valve is fully open to closed supercharging, turbocharging effect will be so affected. It can be determined, is the root cause of the boost pressure control solenoid valve due to filter clogging.

Troubleshooting: 2 blown clean with compressed air the dust on the filter solenoid valve, the solenoid valve installation and clear fault code, the fault disappears road test.

(high Young)

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