Volkswagen Golf Service & Repair Manual: Checking vacuum generation

Note The average air pressure of the earth's atmosphere at sea level is 1013 mbar and decreases steeply as the altitude increases (approx. 100 mbar/1,000 m altitude). Local and time fluctuations also influence vacuum generation. A cold engine, a switched-on air-conditioning system as well as engine idling have an adverse influence on generation of a vacuum.

Before starting work, check all vacuum hoses for damage (e.g. cracks or marten bite) and to check that they are correctly and firmly attached
Connect brake servo vacuum gauge -VAS 6721- → Chapter.
Open cut-off valve -A-.

Close cut-off valves -B+C-.
Start warm engine (>60 °C), press accelerator briefly (engine speed above 2,000 rpm).
Read indicated measured value.

Normally (see notes), the vacuum that is generated should be between 600 and 950 mbar (depending on engine size). If the measured value is not reached even through the preconditions (see notes) have been met, the vacuum system must first be checked for leaks.

For comparison purposes, generate the vacuum with the manual vacuum pump -VAS 6213- → Chapter.

Open cut-off valve -B- to facilitate removal of hose connections and adapter.

Checking vacuum generation

Open cut-off valve -B- to facilitate removal of hose connections and adapter.

Test yourself