Intake Manifold Vacuum; Diagnosis Of Engine Condition By Measurement Of Manifold Vacuum - Subaru SVX 1992 Manual

ON-CAR SERVICES [05AO] 2-2
5 . Intake Manifold Vacuum
A: MEASUREMENT
1) Warm up the engine .
2) Disconnect the vacuum hose and install the vacuum
gauge to the hose fitting on the manifold .
3) Keep the engine at the idle speed and read the
vacuum gauge indication .
By observing the gauge needle movement, the internal
condition of the engine can be diagnosed as described
in Table below.
/ i Vacuum gauge
1 /-
= _,
`
Intake
manifold
til...-
/ 1 ,.~
C2-150
Vacuum pressure (at idling, A/C "OFF") :
More than 68 .0 kPa (510 mmHg, 20 .08 inHg)
Fig . 2
Diagnosis of engine condition by measurement of manifold vacuum
Vacuum gauge indication Possible engine condition
1 . Needle is steady but lower than normal position. This tendency
Leakage around air intake system .
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 Back pressure too high, or exhaust muffler clogged .
normal position.
3 . Needle intermittently drops to position lower than normal posi-
Leakage around cylinder .
tion.
4 . Needle drops suddenly and intermittently from normal position . Sticky valves.
5 . When engine speed is gradually increased, needle begins to vi-
brate rapidly at certain speed, and then vibration increases as Weak or broken valve springs .
engine speed increases .
6 . Needle vibrates above and below normal position in narrow
Defective ignition system or throttle chamber idle adjustment.
range .
3