Section 27 (Engine Mechanical (H4DOTC)): Compression: Inspection

WARNING: This page is about a different car, the 2006 Subaru Outback and 2006 Subaru Legacy. However, it is still accessible from the selected car via links, so may be relevant.

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

Remove the collector cover.
After warming-up the engine, turn the ignition switch to OFF.
Make sure that the battery is fully charged.
Release the fuel pressure. < Ref. to RELEASING OF FUEL PRESSURE , PROCEDURE, Fuel. >
Remove all the spark plugs.
< Ref. to REMOVAL , Spark Plug. >
Fully open the throttle valve.
Check the starter motor for satisfactory performance and operation.
Hold the compression gauge tightly against the spark plug hole.
NOTE: When using a screw-in type compression gauge, the screw (put into cylinder head spark plug hole) should be less than 18 mm (0.71 in) long.
Crank the engine by means of the starter motor, and read the maximum value on the gauge when the pointer is steady.

Fig 1: Checking Compression Using Compression Gauge
Perform at least two measurements per cylinder, and make sure that the values are correct.
Compression (350 RPM and 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