Engine Mechanical System: Compression: Inspection

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

NOTE:

Before checking the compression pressure, the compression condition of each cylinder can be confirmed as a guide by using the cylinder compression measurement mode in Subaru Select Monitor. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>ACTIVE TEST>OPERATION .
In the cylinder compression measurement mode, the compression condition is judged by each cylinder speed. The high speed cylinder has low compression pressure and low speed cylinder has high compression pressure.

After warming-up the engine, turn the ignition switch to OFF.
Make sure that the battery is fully charged.
Check the starter motor for satisfactory performance and operation.
Remove the fuse of fuel pump from main fuse box.

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Start the engine and run it until it stalls.
After the engine stalls, crank it for five more seconds.
Turn the ignition switch to OFF.
Remove all spark plugs. Ref. to IGNITION (H4DO)>SPARK PLUG>REMOVAL .
Install the compression gauge to the spark plug hole.
NOTE: When using a screw-in type compression gauge, the screw should be less than 25 mm (0.98 in) long.

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Connect the connectors to the ECM in numerical order as shown in the figure.
CAUTION: To prevent damage to the connector, when connecting the connector, insert the connector straight in until it stops, and while maintaining the position, lock the lever.

NOTE: When connecting the connector, check that the lever is located at the position shown in the figure (position beyond the lock portion (a)).

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Connect the ground terminal to the battery sensor. Ref. to REPAIR CONTENTS>NOTE>BATTERY .
Turn the ignition switch to ON.
Depress the accelerator pedal to full throttle.
Crank the engine by starter motor and read the value when the needle of the compression gauge becomes stable.
NOTE:
- Perform at least two measurements per cylinder, and make sure that the values are correct.
- If the compression pressure is out of the standard value, check or adjust the pistons, valves and cylinders.
Compression pressure:

At 200 - 300 r/min

Standard

1, 390 - 1, 735 kPa (14 - 18 kgf/cm² , 202 - 252 psi)

Difference between cylinders

100 kPa (1 kgf/cm² , 14 psi) or less
After inspection, install the related parts in the reverse order of removal.
NOTE: When compression pressure is checked, the malfunction indicator light illuminates and DTCs may be stored in ECM. When the malfunction indicator light has illuminated, clear the memory. Ref. to COMMON (DIAGNOSTICS)>CLEAR MEMORY>OPERATION .