The Audi A6L 2.4 car with a mileage of over 224 thousand km in 2005. User response: the vehicle can not be speeded up and will not go on high speed. Fault diagnosis: (1) first use VA56150 to detect fault codes, cylinder blocks 1 and 2 mixture gas is too thick. Check the fuel pressure is normal, the nozzle has no leakage phenomenon, try to replace the spark plug and ignition coil is invalid. The analysis believes that the car has been driving 220 thousand kilometers, three yuan catalytic converter is more likely to be blocked, after inspection found that three yuan catalytic converter is really blocked, change about three yuan catalyst after the test is normal, accelerated failure to troubleshooting, but in the process of washing cars found sometimes start flushing, small fuel valve refueling no car. (2) again test the test to confirm that the fault occurred at low speed or reversing and hitting the direction, using 5052 read data blocks to find the mixer adjustment up to 25%, still have a strong situation, check the carbon tank electromagnetic valve, the signs of tight, the replacement after the failure is still. It has tried to replace nozzle, oxygen sensor and fuel pump, replacing valve and engine control unit. There is no exception to read the data of the gearbox. (3) readjusting the train of thought, because the fault often occurs in the low speed and the direction of the direction, and is doubted whether the engine power is insufficient. After measuring cylinder pressure found 4 cylinder, 5 cylinder, 6 cylinder pressure of about 9BAR, and 1 cylinder, 2 cylinder, 3 cylinder pressure is around 12bar, the analysis of 3 cylinder valves are not likely to appear problems, the endoscopy also found no sign of pulling cylinder, three catalyst has changed, is 1 column intake problem? In order to replace the intake manifold failure, we have to dismantle the engine and find that the ring groove of the 4 cylinder, the 5 cylinder and the 6 cylinder piston is broken and damaged, which causes the cylinder pressure to be low and the replacement of the piston and the ring after the ring is replaced. Troubleshooting: replacement of piston and piston ring. Failure summary: engine power should also be considered when starting failures.