Intake Manifold Vacuum - Subaru IMPREZA 2002 Service Manual

INTAKE MANIFOLD VACUUM
MECHANICAL
Vacuum gauge indication
1. Needle is steady but lower than normal position. This ten-
dencv becomes more evident as engine temperature rises.
3) Keep the engine at the idle speed and read the
vacuum gauge indication.
A: INSPECTION
By observing the gauge needle movement, the in-
1) Warm-up the engine.
ternal condition of the engine can be diagnosed as
5. Intake Manifold Vacuum
Possible engine condition
Leakage around intake manifold gasket or disconnection or
damaged vacuum hose
2) Disconn.ect the brake vacuum hose and install
the vacuum gauge to the hose fitting on the mani-
fold.
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.
described below.
Back pressure too high, or exhaust system clogged
Leakage around cylinder
Vacuum pressure (at idling, A/C
c 6 0 F F ) :
Less than -60.0 kPa (-450 mmHg, -17.72 in-
Hg)
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.
Diagnosis of engine condition by measurement of manifold vacuum
Sticky valves
Weak or broken valve springs
Defective ignition system or throttle chamber idle adjustment
ME(S0HC)-26