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Intake Manifold Vacuum: Inspection

  1. Remove the collector cover. Ref. to INTAKE (INDUCTION) (H4DO)>COLLECTOR COVER>REMOVAL .
  2. Warm up the engine.
  3. Disconnect the brake booster vacuum hose from the intake manifold assembly.
    G13224240Courtesy of SUBARU OF AMERICA, INC.
  4. Connect the vacuum gauge to the installation area for the brake booster vacuum hose of the intake manifold assembly.
    G10262497Courtesy of SUBARU OF AMERICA, INC.
  5. Keep the engine at idle speed and read the vacuum gauge indication.
    NOTE: Condition of engine inside can be diagnosed by observing the behavior of the vacuum gauge needle as described in table below.
    DIAGNOSIS OF ENGINE CONDITION BY INSPECTION OF INTAKE MANIFOLD VACUUM

    Vacuum gauge needle behavior Possible engine condition
    1. Needle is steady but lower than standard value. This tendency becomes more evident as engine temperature rises.
    		 Leakage around intake manifold gasket, disconnection or damage of vacuum hose
    2. Needle intermittently drops below the standard value. Leakage around cylinder
    3. Needle drops suddenly and intermittently from the standard value. Sticky valve
    4. When engine speed is gradually increased, needle begins to vibrate rapidly at certain speed, and then vibration increases as engine speed increases. Weak or broken valve springs
    5. Needle vibrates above and below the standard value in narrow range. Defective ignition system

    Intake manifold vacuum (A/C is at idling, A/C OFF): 

    Standard 

    -60.0 kPa (-450 mmHg, -17.72 inHg) or more

  6. After inspection, install the related parts in the reverse order of removal.
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