BMW 740n55 engine gear car gasps.

Poor air intake or poor exhaust. Check whether the air filter is too dirty or the throttle has too much carbon. If there is no problem, check whether the three-way catalyst is not blocked.

This abnormal sound generally has the following characteristics.

1, and the vehicle mileage is generally more than 50,000 kilometers.

2. Abnormal noise mostly occurs in the initial stage after a period of high-speed driving, and then occurs at idle speed.

3. Harsh whistles, whistles, squeaks and creaks can be heard inside and outside the car.

4. Open the filler cap and the noise disappears; Close the oil filler cap and the noise reappears.

5. Abnormal sound generally only appears at idle speed or near idle speed, and will gradually decrease or basically disappear with the increase of rotating speed.

If the fault phenomenon of your car conforms to the above description, 90% is caused by crankshaft oil seal, so you can listen carefully to the sound source. If the abnormal noise comes from the rear of the engine, it is the abnormal noise generated by the crankshaft rear oil seal. If the abnormal noise comes from the front of the engine, it is the abnormal noise generated by the front oil seal of the crankshaft. The cause of abnormal sound

More than 95% of abnormal noise produced by crankshaft oil seal is caused by the damage of waste gas valve on valve cover and excessive negative pressure of crankcase at idle speed. Maintenance scheme

You can use a vacuum tube to blow air into the exhaust port of the waste gas valve. If it can be blown through, it can be judged more accurately by measuring the pressure in the crankcase. The exhaust valve of BMW N55 engine is integrated on the valve cover, and the valve cover needs to be replaced during maintenance. Very few valve covers still have abnormal sound after replacement, which does not mean that the valve cover has been replaced incorrectly. The main reason is that the long-term negative pressure in the crankcase is too large after the waste gas valve is damaged, which leads to the damage of crankshaft oil seal. Usually, at present, this fault has been repaired by several sets, and it can be solved by replacing the valve cover.