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Section 10 (Engine Mechanical): Compression: Inspection

WARNING: This page is about a different car, the 2015 Subaru XV Crosstrek and 2015 Subaru Impreza. 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.
  1. Turn the ignition switch to OFF.
  2. Remove the collector cover. (HEV model)
    1. Carefully pull up the front of collector cover at two positions (A).
    2. Carefully pull up the rear of collector cover at two positions (B) while moving it backward.
    NOTE: Be careful not to contact the fuel delivery tube when moving the collector cover rearward.
    Fig 1: Removing Collector Cover (HEV Model)
    G09486016Courtesy of SUBARU OF AMERICA, INC.
  3. After warming-up the engine, turn the ignition switch to OFF.
  4. Make sure that the battery (12 volt auxiliary battery) is fully charged.
  5. Check the starter motor for satisfactory performance and operation.
  6. Remove the fuse of fuel pump from main fuse box.
    Fig 2: Locating Fuel Pump Fuse
    G09486017Courtesy of SUBARU OF AMERICA, INC.
  7. Start the engine and run it until it stalls.
  8. After the engine stalls, crank it for five more seconds.
  9. Turn the ignition switch to OFF.
  10. Remove all spark plugs. < Ref. to REMOVAL , Spark Plug.>
  11. 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
    G09486018Courtesy of SUBARU OF AMERICA, INC.
  12. Install the 12 volt engine restart battery. (HEV model) < Ref. to 12 VOLT ENGINE RESTART BATTERY , INSTALLATION, Battery.>
  13. Connect the battery ground terminal. < Ref. to BATTERY , NOTE, Note.>
  14. Turn the ignition switch to ON.
  15. Depress the accelerator pedal to full throttle.
  16. 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 kg/cm 2  , 152 - 203 psi) 

    Difference between cylinders 100 kPa (1 kg/cm 2  , 14 psi), or less 

  17. After inspection, install the related parts in the reverse order of removal.
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