Subaru Legacy BN/BS (2015-2019) Service Manual: Intake manifold vacuum inspection

Subaru Legacy BN/BS (2015-2019) Service Manual / Mechanical(h4do) / Intake manifold vacuum inspection

1. Warm up the engine.

2. Disconnect the brake booster vacuum hose from the intake manifold assembly.

3. Connect the vacuum gauge to the installation area for the brake booster vacuum hose of the intake manifold assembly.

4. 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 (at idling, A/C OFF):

Standard

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

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 to position lower than standard value.	Leakage around cylinder
3. Needle drops suddenly and intermittently from 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 standard value in narrow range.	Defective ignition system

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

Intake and exhaust valve specification

Refer to “Cylinder Head” for removal and installation procedures of the intake and exhaust valves. Cylinder Head > REMOVAL Cylinder Head > INSTALLATION ...

Piston specification

Refer to “Cylinder Block” for removal and installation procedures of pistons. Cylinder Block > REMOVAL Cylinder Block > INSTALLATION ...

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