Intake Manifold Vacuum - Subaru Legacy 2004 Service Manual

5. Intake Manifold Vacuum

A: INSPECTION
1) Idle the engine.
2) Disconnect the brake vacuum hose from the in-
take manifold, and then install the vacuum gauge.
3) Keep the engine at the idle speed and read the
vacuum gauge indication.
By observing the gauge needle movement, the in-
ternal condition of the engine can be diagnosed as
described below.
Vacuum pressure (at idling, A/C "OFF"):
%
Less than 60.0 kPa (
Hg)
Diagnosis of engine condition by measurement of intake manifold vacuum
Vacuum gauge indication
1. Needle is steady but lower than normal position. This ten-
dency becomes more evident as engine temperature rises.
2. When engine speed is reduced slowly from higher speed,
needle stops temporarily when it is lowering or becomes steady
above normal position.
3. Needle intermittently drops to position lower than normal
position.
4. Needle drops suddenly and intermittently from normal posi-
tion.
5. When engine speed is gradually increased, needle begins to
vibrate rapidly at certain speed, and then vibration increases as
engine speed increases.
6. Needle vibrates above and below normal position in narrow
range.
Intake Manifold Vacuum
ME-00813
% %
450 mmHg, 17.72 in-
ME(H4SO 2.0)-25
Possible engine condition
Air leakage around intake manifold gasket, disconnection or
damage of vacuum hose
Exhaust pressure is too high, or exhaust system is clogged.
Leakage around cylinder
Valve anchoring
Weak or broken valve springs
Defective ignition system
MECHANICAL