Vacuum Pump: Testing and Inspection

WM 477601 Checking vacuum pump

Tools






Information

The vacuum pump creates the necessary vacuum for the following components and functions:

- The variable intake system on naturally aspirated engines (secondary load).

- Sports flap exhaust system (secondary load).

- The tank leakage test on US vehicles (secondary load).

- Wastegate control on turbo vehicles (secondary load).

- Brake booster (main load - large connection)

Defects in the specified systems can be caused by a defective vacuum pump. To avoid replacing components based on suspected defects and repeat repairs, the function of the vacuum pump must be checked.

The vacuum pump -1- is fitted at the rear of the right cylinder head on V-engines.





Vacuum pump (mechanical)





Vacuum pump with connections






Checking vacuum pump

Information

This check mainly involves examining the secondary load connection due to problems. The main connection (brake booster) is not checked. Defects in the main connection would be apparent immediately due to increasing pedal forces during braking (similar to a defective brake booster).

1. Expose the secondary load connection of the vacuum pump -5-. Different preliminary work is required, depending on the model and equipment variant.





Vacuum pump with connections





2. Connect vacuum gauge tester 9160/1 to the secondary load connection.
3. Set vacuum gauge tester 9160/1 to vacuum (lever in open position).
4. Start engine and run it at idle speed with slightly changing revs.
5. The vacuum pump must create a vacuum of at least 500 mbar or 0.5 bar.
6. If the vacuum is not maintained, i.e. the pointer moves towards 0, the vacuum pump is defective. Replace the vacuum pump. For details, see => 477619 Removing and installing vacuum pump
7. This defect can cause engine oil to get into the vacuum system. In this case, the lines and switching valves must be checked visually and replaced if necessary or cleaned with solvent naphtha.