A Mercedes Benz S280 with a mileage of about 143000 km. When the vehicle speed is below 100km / h, the acceleration is normal; when the vehicle speed is above 100km / h, the acceleration is weak, and the engine warning light gives an alarm. Engine idle jitter in place, turn off the ignition switch and start again, engine idle jitter disappears.

故障诊断：启动发动机观察运转情况，怠速转速750r/min无抖动，加速到2000r/min无抖动，加速到3500r/min无抖动。在高速公路上试车，车速在100km/h以下加速有力，车速在100km/h以上加速坐车，停车后出现发动机怠速抖动。

No engine speed jitter was detected at 20 000 R / 750 min, no engine speed jitter was detected during acceleration. In the test run on the highway, when the speed is below 100km / h, the acceleration is powerful, when the speed is above 100km / h, the engine idling jitter occurs after parking.

用诊断仪检测存储当前故障码“3缸、6缸失火”，读取实际值“3缸、6缸失火超过失火限值”，已不能点火，读取喷油时间为3.6～3.8ms，标准为2.7～4.2msa

Use the diagnostic instrument to detect and store the current fault code "misfire of cylinder 3 and 6", read the actual value "misfire of cylinder 3 and 6 exceeds the misfire limit", and the ignition can not be started. The read injection time is 3.6 ~ 3.8ms, and the standard is 2.7 ~ 4.2msa

拆卸3缸、6缸点火线圈检查未发现异常，拆卸火花塞检查发现电极间隙较大。测量所有汽缸压力均为1100kPa，符合要求。测量发动机控制模块到3缸、6缸点火线圈的导线电阻为0.2Ω，符合要求。更换全部火花塞，将3缸、6缸点火线圈与2缸、5缸互换，路试故障现象依旧，故障码仍是“3缸、6缸失火”。

No abnormality was found after the ignition coils of cylinder 3 and 6 were disassembled, and large electrode gap was found after the spark plug was disassembled. All cylinder pressures measured are 1100kpa, meeting the requirements. The wire resistance from the engine control module to the ignition coil of cylinder 3 and 6 is 0.2 Ω, which meets the requirements. All spark plugs were replaced, and the ignition coils of cylinder 3 and 6 were exchanged with those of cylinder 2 and 5. The road test showed that the fault still existed, and the fault code was still "cylinder 3 and 6 are on fire".

测量燃油压力，怠速为380kPa、急加速时压力降340kPa，然后迅速提升到420kPa。拆开三元催化器连接处，用内窥镜观察蜂窝状陶瓷载体透气良好。

The fuel pressure is measured. The idle speed is 380kpa, the pressure drops to 340kpa during rapid acceleration, and then rises to 420kpa rapidly. The connection of the three-way catalytic converter was disassembled, and the honeycomb ceramic carrier was observed by endoscope.

清洗节气门、喷油器，路试加速性能有好转，但加速性能仍不正常，高速行驶停车后发动机出现抖动，故障码只是“6缸失火”。将6缸与2缸的喷油器互换，路试仍是高速加速无力，故障码仍是“6缸失火”。

After cleaning the throttle and fuel injector, the acceleration performance of the road test is improved, but the acceleration performance is still abnormal. The engine shakes after parking at high speed, and the fault code is "cylinder 6 misfire". If the injector of cylinder 6 and cylinder 2 are interchanged, the high-speed acceleration is still weak in the road test, and the fault code is still "cylinder 6 misfire".

通过多次试车，该车低速加速动力正常，高速加速明显无力，怀疑燃油泵工作不正常。做燃油泵供油量测试，运转40s泵油1L，达到标准值的下限。对正常车辆做燃油泵供油量测试，测试结果高出1L很多。

After many tests, the low-speed acceleration power of the car is normal, and the high-speed acceleration is obviously weak. It is suspected that the fuel pump is not working properly. Test the fuel supply quantity of the fuel pump, run for 40s, Pump Oil 1L, reach the lower limit of the standard value. The test result of fuel supply quantity of normal vehicle is much higher than 1L.

故障排除：更换燃油泵，接上燃油压力表，观察原地加速时燃油压力没有下降现象。试车，高速加速性能正常，故障排除。

Troubleshooting: replace the fuel pump, connect the fuel pressure gauge, and observe that the fuel pressure does not drop when accelerating in situ. Test run, high speed acceleration performance is normal, troubleshooting.

故障总结：此车为软故障，测量此车燃油压力为标准值的下极限，如果不与正常车辆数据对比察觉不出异常，通过对比找到软故障的原因所在。

Fault summary: this car is a soft fault. The fuel pressure of this car is measured as the lower limit of the standard value. If there is no abnormality detected by not comparing with the normal vehicle data, the cause of the soft fault can be found through comparison.