A Mercedes 600SEL car with a mileage of over 250 thousand km, a M120 engine and an automatic transmission, and a chassis model of W140. The malfunction of the car is that the engine idling is basically normal, but the exhaust pipe runs black smoke when it accelerates to 1500 ~ 3000r/min. The M120 engine is a V12 engine with two sets of ignition components. To confirm the fault symptoms, when the engine speed rises from 1500r/min to 3000r/min, the acceleration of the vehicle is weak and the acceleration failure is more obvious. But the engine speed is over 3000r/min, and the acceleration performance is restored to normal. Connect the diagnostic device for self diagnosis without fault code. The fuel pressure is measured, and the fuel pressure at idle condition is 330kPa. Unplug the vacuum tube of the fuel pressure regulator and change the fuel pressure to 390kpa. The above inspection results indicate that the fuel pressure is normal. It is normal to measure the resistance of two ignition coils. The resistance of all high voltage lines is measured in the range of standard values. Clean the fuel injector, replace the fuel filter and spark plug. The test run is still in trouble. Check the gas distribution phase, no problem. Starting the engine, pulling the camshaft off the camshaft to adjust the wire harness plug of the solenoid valve at the idle condition, the engine condition has changed, indicating that the variable timing camshaft adjustment device is normal. The pressure of all cylinders is measured within the standard value range. Check the exhaust status, the left exhaust is uniform, the right exhaust has intermittent stop phenomenon, and the right exhaust pipe temperature is obviously higher than the left exhaust pipe, indicating that the right column cylinder is not working. Replace the ignition coil on the left and right columns, and the result is that the cylinder is not working correctly. The engine speed is stabilized at 2000r/min, and the high pressure line of the right column cylinder is pulled out one by one. Every high pressure line is pulled down, and the engine speed is not obvious. When the left cylinder is inspected, every engine pulls down a high voltage line, and the engine speed drops obviously. In order to verify whether the fault is related to the ignition energy, the high pressure line of a right column cylinder and the high pressure line of a left column cylinder are removed respectively, and the spark plug is inserted to observe the situation of the fire. When the engine speed reached 1500r/min, the spark plug ignition energy began to weaken when the engine speed reached 1500r/min, and the spark plug ignition of the right column cylinder returned to normal when the engine speed was to 3000r/min. Replace the ignition control module on the right cylinder, and remove the trouble completely. The fault of this case has certain particularity. The ignition control module of the right column cylinder has not been completely damaged, but it works well in a certain range of engine speed, the specific reason is that the internal ignition output pole is not good. It is necessary to explain that, although the ignition control module has fault monitoring functions, it can not monitor its own ignition output circuit and external executor, so it does not store the related information of such faults.