Cherokee 4WD L6-242 4.0L VIN S MFI (1992)
1. Connect a vacuum gauge to the booster check valve with a short length of hose and a T-fitting.
2. Start and run engine at idle speed for one minute.
3. Clamp hose shut between vacuum source and check valve.
4. Stop engine and observe vacuum gauge.
5. If vacuum drops more than one inch HG (33 millibars) within 15 seconds, booster diaphragm or check valve is faulty.
