Subaru Legacy IV (2008 year). Manual - part 260

ME(H4DOTC)-20

Compression

MECHANICAL

2. Compression

A: INSPECTION

CAUTION:
After warming-up, engine becomes very hot. Be
careful not to burn yourself during measure-
ment.
1) Remove the collector cover.
2) After warming-up the engine, turn the ignition
switch to OFF.
3) Make sure that the battery is fully charged.
4) Release the fuel pressure. <Ref. to
FU(H4DOTC)-57, RELEASING OF FUEL PRES-
SURE, PROCEDURE, Fuel.>
5) Remove all the spark plugs.
<Ref. to IG(H4DOTC)-4, REMOVAL, Spark Plug.>
6) Fully open the throttle valve.
7) Check the starter motor for satisfactory perfor-
mance and operation.
8) Secure the compression gauge tightly against
the spark plug hole.

NOTE:
When using a screw-in type compression gauge,
the screw should be less than 18 mm (0.71 in) long.
9) Crank the engine by the starter motor, and read
the maximum value on the gauge when the needle
of gauge is steady.

10) Perform at least two measurements per cylin-
der, and make sure that the values are correct.

Compression (fully open throttle):

Standard:

981 — 1,177 kPa 
(10 — 12 kgf/cm

2

, 142 — 171 psi)

Difference between cylinders:

49 kPa (0.5 kgf/cm

2

, 7 psi) or less

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

ME-03009

ME(H4DOTC)-21

Idle Speed

MECHANICAL

3. Idle Speed

A: INSPECTION

1) Before checking the idle speed, check the fol-
lowing item:

(1) Check the air cleaner element is free from
clogging, ignition timing is correct, spark plugs
are in good condition, and hoses are connected
properly.
(2) Check the malfunction indicator light does
not illuminate.

2) Warm up the engine.
3) Read the engine idle speed using Subaru Select
Monitor. <Ref. to EN(H4DOTC)(diag)-35, READ
CURRENT DATA FOR ENGINE (NORMAL
MODE), OPERATION, Subaru Select Monitor.>
4) Check the idle speed when no-loaded. (Head-
light, heater fan, rear defroster, radiator fan, A/C
and etc. are OFF)

Idle speed [No load and gear in neutral, or “P”, 
“N” range]:

750

r

100 rpm

5) Check the idle speed when loaded. (Turn the A/
C switch to “ON” and operate the compressor for at
least one minute before measurement.)

Idle speed [A/C ON and gear in neutral or “P” or 
“N” range]:

800

r

100 rpm (MT model)

825

r

100 rpm (AT model)

NOTE:
Idle speed cannot be adjusted manually, because
the idle speed is automatically adjusted. If the pre-
scribed idle speed cannot be maintained, refer to
the General On-board Diagnosis Table under “En-
gine Control System”. <Ref. to EN(H4DOTC)(di-
ag)-2, Basic Diagnostic Procedure.>

ME(H4DOTC)-22

Ignition Timing

MECHANICAL

4. Ignition Timing

A: INSPECTION

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

1. METHOD WITH SUBARU SELECT 
MONITOR

1) Before checking the ignition timing, check the
following item:

(1) Check the air cleaner element is free from
clogging, spark plugs are in good condition, and
hoses are connected properly.
(2) Check the malfunction indicator light does
not illuminate.

2) Warm up the engine.
3) Read the ignition timing using Subaru Select
Monitor. <Ref. to EN(H4DOTC)(diag)-35, READ
CURRENT DATA FOR ENGINE (NORMAL
MODE), OPERATION, Subaru Select Monitor.>

Ignition timing [BTDC/rpm]:

12°

r

10°/750 (MT model)

17°

r

10°/750 (AT model)

If the timing is not correct, check the ignition control
system. Refer to “Engine Control System”. <Ref. to
EN(H4DOTC)(diag)-2, Basic Diagnostic Proce-
dure.>

2. METHOD WITH TIMING LIGHT

1) Before checking the ignition timing, check the
following item:

(1) Check the air cleaner element is free from
clogging, spark plugs are in good condition, and
hoses are connected properly.
(2) Check the malfunction indicator light does
not illuminate.

2) Warm up the engine.
3) Stop the engine, and turn the ignition switch to
OFF.
4) Remove the air intake duct. <Ref. to
IN(H4DOTC)-9, REMOVAL, Air Intake Duct.>
5) Disconnect the connectors of the mass air flow
and intake air temperature sensor.
6) Remove the air cleaner case and element.
7) Connect the timing light to the power wire of #1
ignition coil.
8) Install the connectors of air cleaner case, ele-
ment, and the mass air flow and intake air temper-
ature sensor.
9) Start the engine, turn the timing light to the crank
pulley, and check the ignition timing by means of
crank pulley indicator.

Ignition timing [BTDC/rpm]:

12°

r

10°/750 (MT model)

17°

r

10°/750 (AT model)

If the timing is not correct, check the ignition control
system. Refer to “Engine Control System”. <Ref. to
EN(H4DOTC)(diag)-2, Basic Diagnostic Proce-
dure.>

ME(H4DOTC)-23

Intake Manifold Vacuum

MECHANICAL

5. Intake Manifold Vacuum

A: INSPECTION

1) Remove the collector cover.
2) Warm up the engine.
3) Disconnect the brake booster vacuum hose from
the intake manifold, and then install the vacuum
gauge.
4) Keep the engine at idle speed and read the vac-
uum 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 –70.6 kPa 
(–530 mmHg, –20.85 inHg) (MT model)
Less than –68.0 kPa 
(–510 mmHg, –20.08 inHg) (AT model)

ME-00801

Diagnosis of engine condition by measurement of intake manifold vacuum

Vacuum gauge indication

Possible engine condition

1. Needle is steady but lower than normal position. This tendency 
becomes more evident as engine temperature rises.

Leakage around intake manifold gasket, or disconnected 
or damaged vacuum hose

2. Needle intermittently drops to position lower than normal position.

Leakage around cylinder

3. Needle drops suddenly and intermittently from normal position.

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 normal position in narrow range. Defective ignition system