The mileage is over 230 thousand km, with 2004 Buick Regal 2.0L cars equipped with L34 engines. The car smoked in front of the hill and asked for relief. When the maintenance personnel arrive at the vehicle site, the machine cover is found to have leakage of oil from the valve chamber cover (upper part of the exhaust pipe) and leaked on the exhaust pipe. After inquiring the customer, the vehicle has been regularly maintained, and the valve chamber cover has been replaced for 3 times, but the malfunction is becoming more and more serious. Fault diagnosis: because the car has changed 3 valve chamber cover pads, and each time from the same place out of oil, after dismantling, carefully observe the location of oil channeling, valve chamber cover card cushion card slot larger than other places, and the previous few times have not covered with sealing glue. After the customer agrees, replace the mattress again and apply the sealant. After idle and emergency refueling, no signs of oil leakage are found. When the road test vehicle was running, the blue smoke came out of the same oil leak soon after, and the maintenance personnel extinguished it in time. After starting the vehicle, there was no oil channeling. Careful analysis, the reasons for this situation are as follows: excessive exhaust gas in the crankcase, excessive pressure of exhaust gas, large gas flow rate of piston ring, abnormal operation of crankcase PCV system, poor sealing of valve chamber cover and so on. Pull out the crankcase ventilation inlet, test the vehicle and return to normal. At this point, the possibility that the valve chamber cover is broken is very low. Ask the customer to know that there is no oil burning phenomenon. The speed of the vehicle is very good and the possibility of removing the piston ring is very high. Then, we can only start with the PCV system, and remove the outlet outlets of the two valve chambers, one leading to the front of the throttle, and one toward the rear of the throttle. When the inlet of the crankcase ventilation pipe is reassembled, the test run should normally be able to cover the exhaust valve from the valve chamber, but this vehicle does not. After the valve cover is removed, it is found that the vent pipe inside the valve chamber is blocked by carbon deposit. After stabbing with wire, test the car and troubleshooting. Maintenance summary: because the 2.0L engine crankcase ventilation valve is integrated with the valve chamber cover, the exhaust gas of the crankcase can not be discharged in time. After the system pressure is too high, it is very easy to run out from the weakest place, and the oil is leaking out at the same time. So in the maintenance of the vehicle's day training Wu, do not blindly replace the accessories, to be comprehensive. Check it over so that we can discover new problems.