Section 178 (Engine Mechanical (H4DOTC)): Compression: Inspection

WARNING: This page is about a different car, the 2004 Subaru Baja. 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.

After warming-up the engine, turn the ignition switch to OFF.
Make sure that the battery is fully charged.
Release the fuel pressure. Refer to RELEASING OF FUEL PRESSURE , OPERATION, Fuel.
Remove all the spark plugs. Refer to REMOVAL , Spark Plug.
Fully open the throttle valve.
Check the starter motor for satisfactory performance and operation.
Hold the compression gauge tight against 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 starter motor, and then read the maximum value on the gauge when the pointer is steady.

Fig 1: Holding Compression Gauge
Courtesy of SUBARU OF AMERICA, INC.
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/cm² , 142 - 171 psi)

Limit

882 kPa (9.0 kgf/cm² , 128 psi)

Difference between cylinders

Less than 49 kPa (0.5 kgf/cm² , 7 psi)