3 vacuum supply inspection
If the boost function of the vacuum booster is lost or the boosting effect is weak during braking, besides checking the vacuum booster, the vacuum source for supplying the vacuum to the booster and its vacuum line should be inspected. During the inspection, pull out the vacuum booster vacuum connector, start the engine to idle speed, and quickly seal the vacuum nozzle with your thumb. If there is a strong suction at this time, it indicates that the vacuum provided by the engine is sufficient and the vacuum line is normal; if there is no strong suction or no suction at all, the engine should be turned off to check if the vacuum line is damaged, curled, loose or blocked. If the vacuum line is damaged, it should be replaced; if the vacuum line is normal, vacuum gauge is used to check the vacuum degree of the intake manifold when the engine is idling. When the engine is normal, the vacuum gauge reading should be in the range of 40~67 kPa.
If the vacuum pocket is small, there is a problem with the engine providing the vacuum source. The failure of the vacuum source to provide a vacuum pocket is often overlooked, leading to erroneous diagnosis of the vacuum booster and even the replacement of the vacuum booster, which should be noted.