Section 11 (Engine Mechanical (H4DO)): Compression: Inspection

WARNING: This page is about a different variant/trim than selected.

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

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.

Fig 1: Locating Fuel Pump Fuse
Courtesy of SUBARU OF AMERICA, INC.
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. < Refer to REMOVAL , Spark Plug. >
Connect the battery ground terminal.

Fig 2: Connecting/Disconnecting Battery Ground Terminal
Courtesy of SUBARU OF AMERICA, INC.
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.

Fig 3: Installing Compression Gauge To Spark Plug Hole
Courtesy of SUBARU OF AMERICA, INC.
Turn the ignition switch to ON.
Fully open the throttle valve.
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 standard, check or adjust the pistons, valves and cylinders.
Compression (fully open throttle):

Standard

1, 050 - 1, 400 kPa (11 - 14 kgf/cm ² , 152 - 203 psi)

Difference between cylinders

100 kPa (1 kgf/cm ² , 14 psi) or less
After inspection, install the related parts in the reverse order of removal.