Intake Manifold Vacuum: Inspection

CAUTION: After warming-up, engine becomes very hot. Be careful not to burn yourself at measurement.

Remove the generator. Ref. to STARTING/CHARGING SYSTEMS (H4DOTC)>Generator>REMOVAL .
Disconnect the vacuum hose from intake manifold assembly.

Courtesy of SUBARU OF AMERICA, INC.
Connect the vacuum gauge to the installation area for the vacuum hose of the intake manifold assembly.

Courtesy of SUBARU OF AMERICA, INC.
Install the generator. Ref. to STARTING/CHARGING SYSTEMS (H4DOTC)>Generator>INSTALLATION .
Warm up the engine.

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.

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

Standard

-73.4 kPa (-550 mmHg, -21.68 inHg) or more

Diagnosis of engine condition by inspection of intake manifold vacuum
Vacuum gauge needle behavior	Possible engine condition
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