Running about 76 thousand km of the Mercedes Benz AMG ML63. User response: the engine trouble lamp on the meter is always bright. Fault diagnosis: when the engine is tested, the engine can start normally, run smoothly, and have strong driving power without any abnormalities. This car assembly AMG V8 naturally aspirated multi point fuel injection engine, code 156980, compared to the 273 engine, the largest difference in the fuel supply system is equipped with two electric fuel pumps, left fuel pump (M3/2), right fuel pump (M3) and two fuel pump control modules (N118/3 left fuel pump control module, N118/4 right The control module of the side fuel oil pump, as shown in Figure 1. The objective of this system is to provide sufficient fuel under the operating conditions with sufficient pressure (injection pressure) from the fuel tank for the injector. The fuel pump sucks fuel from the fuel supply module through the fuel filter (the fuel filter). The fuel pump draws the fuel from the right fuel tank through the oil suction injection pump, and the fuel pump then pumps the fuel to the fuel distribution rail through the check valve and the fuel filter (single pipe system, also called no return system). In this process, the fuel pressure is limited to about 600kPa by the pressure limiting valve. The check valve is located at the fuel inlet of the fuel filter to prevent fuel pressure from dropping when the fuel pump is off. The oil return from the pressure limiting valve and the part of the fuel supply from the fuel pump provide fuel for the oil suction jet pump in the left fuel tank, transporting the fuel from the left fuel tank chamber to the oil supply module (the right fuel tank chamber). The system is controlled and monitored by the engine control module (N3 / 10) and the fuel pump control module. When the fuel pump control module receives the ground signal from the engine fuel control module, the fuel pump is turned on. The engine control module detects the current fuel pressure from the voltage signal from the fuel pressure sensor (B4/15) to control the fuel pump, the engine control module evaluates the fuel pressure and load requirements, and transfers the "prescribed fuel pressure" pulse width modulation (PWM) signal (the duty ratio of 10% to 90%) to the fuel pump. Control module. The fuel pump control module evaluates the pulse width modulation (PWM) signal and operates the fuel pump at different speeds as required by the pulse width modulation (PWM) signal to make the actual fuel pressure value equal to the set value. According to the fuel requirements, the fuel pressure varies from 400 to 450kPa. The two sets of fuel pumps and their control modules are parallel, and the control data are identical and completely synchronous. Connecting STAR-D for rapid testing, the engine control module (N3/10) set a current state of the fault code: 3699 Fuel pressure control:The upper limit value is reached. (P0191 fuel pressure control to reach the upper limit). None of the two fuel pump control modules has any fault codes. Try to delete the fault code, but as soon as the engine is started, the engine control module will reset the 3699 fault code immediately. According to the working principle of the system and the fault code of the vehicle 3699, the possible reasons for the failure are as follows: (1) blockage of fuel filter; (2) fuel pipeline deformation or blockage; (3) fuel pump wear; (4) damage of fuel pump control module; (5) fuel pressure sensor (B4/15) signal distortion or line fault; (6) engine control module damage . The fuel pressure gauge is connected to the fuel guide, and the actual value of the fuel pressure (absolute value) of the engine control module is 462.6kPa through STAR-D at idle speed, and the PWM correction factor of the fuel pump control module is 24.3%. The standard pressure (absolute value) of the fuel pressure sensor B4/15 (absolute value) at idle speed at the STAR-D diagnosis system is 460kPa, and the readings on the fuel pressure gauge are about 360kPa, and all are normal. The electrical conductors and connections of the fuel pressure sensor have not detected bad contact and corrosion; it shows that the actual fuel pressure and the fuel pressure sensor on the fuel rail can be basically eliminated; the next step determines whether the output of the fuel pump is normal and the fuel pump current intensity at the idle speed of the fuel pump control module. For 18mA, normal; the oil pump measured by the dismantling fuel pump is 1.1 omega and 1 Omega respectively, both less than 2 Omega, the plug has no bad contact and corrosion, normal; the fuel pump output test program in the STAR-D diagnosis system, the oil pipe on the fuel rail is dismantled and inserted into the measuring vessel, and the two fuel pump 8s is promoted. The measured fuel quantity released is only about 0.1L, while the standard value provided by the diagnostic system is greater than 0.5L, indicating that the amount of oil transported is obviously insufficient. There is no collision trace on the bottom of the vehicle. All fuel pipes have no traces of deformation or bending. When the fuel pump is removed, impurities in the fuel tank are not many, and the oil pipes in the combustion chamber are not falling or bent. Check the maintenance record of the car: replace the fuel filter before about 12000km. Comprehensive analysis, the cause of the failure is likely to be the internal wear of the fuel pump resulting in insufficient oil delivery. When the new electric fuel pump is replaced, the oil volume is remeasured. The result is about 0.2L/8s, which is twice as high as that before the replacement, but it is still a 3699 fault code set at a start. In order to eliminate the blockage of the fuel filter, it is decided to replace the fuel filter at the same time. Troubleshooting: after replacing the new fuel filter and fuel pump, re measuring the oil delivery, the result is 0.3L/8s, although the diagnostic system still does not provide the standard value greater than 0.5L, but the fault light is not bright, fault code 3699 no longer appears, various road condition test cars after 20km confirm the fault has been ruled out. Fault summary: the inspection of the fuel supply system should be comprehensive. In addition to checking the pressure of burning Shantou (including the oil pressure on each working condition, keeping pressure), the resistance of the fuel pump and the upper current, the output of the fuel pump should also be checked, and the low output will also affect the adjustment of the air fuel ratio, and the fault code will be set when the fuel pump is too small.