Vacuum, Checking
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- The average earth atmospheric air pressure at sea level (N. N.) is 1013 mbar (15 psi) and it decreases dramatically at higher altitudes (approximately 100 mbar (1.5 psi) every 1000 meters higher (3280 ft)) Local and time fluctuations also influence the vacuum.
- A cold engine, the A/C switched on as well as the engine simply idling can negatively influence the vacuum.
-- Connect the Brake Servo Tester: VAS6721 . Refer to BRAKE BOOSTER TESTER, CONNECTING .
-- Open the shut-off valve -A-.
-- Close the shut-off valves -B and C-.
-- Start the warm (above 60 °C) engine and press the accelerator pedal one time quickly (engine speed higher than 2, 000 RPM).
-- Read the displayed measured value.
- Normally (see note), the vacuum should be between 600 and 950 mbar (9 and 13 psi) (depending on the engine installed).
- Check the vacuum system for leaks if the measured value is not reached, even though all requirements (see notes) are met.
-- Create a vacuum using the Hand Vacuum Pump: VAS6213 for comparison. Refer to VACUUM, CREATING WITH HAND VACUUM PUMP .
-- Opening the shut-off valve -B- makes it easier to remove the hose connections and the adapter.