Mechanical (H4SO): Compression: Inspection

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.
Remove the fuse of fuel pump from main fuse box.

Fig 1: Locating Main Fuse Box
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
Fully open the throttle valve.
Check the starter motor for satisfactory performance and operation.
Install the compression gauge to 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.

Fig 2: Installing Compression Gauge To Spark Plug Hole
Courtesy of SUBARU OF AMERICA, INC.
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, 20 - 1, 75 kPa (10.4 - 13.0 kgf/cm ² , 148 - 185 psi)
  
  Difference between cylinders
  
  49 kPa (0.5 kgf/cm ² , 7 psi) or less
After inspection, install the related parts in the reverse order of removal.