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Engine Mechanical System: Compression: Inspection

CAUTION: After warming-up, engine becomes very hot. Be careful not to burn yourself during measurement.
NOTE:
  • Before checking the compression pressure, the compression condition of each cylinder can be confirmed as a guide by using the compression measurement mode in Subaru Select Monitor. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>ACTIVE TEST>OPERATION .
  • In the compression measurement mode, the compression condition is judged by each cylinder speed. The high speed cylinder has low compression pressure and low speed cylinder has high compression pressure.
  1. After warming-up the engine, turn the ignition switch to OFF.
  2. Make sure that the battery is fully charged.
  3. Check the starter motor for satisfactory performance and operation.
  4. Remove the fuse of fuel pump from main fuse box.
    G13223999Courtesy of SUBARU OF AMERICA, INC.
  5. Start the engine and run it until it stalls.
  6. After the engine stalls, crank it for five more seconds.
  7. Turn the ignition switch to OFF.
  8. Remove all spark plugs. Ref. to IGNITION (H4DO)>SPARK PLUG>REMOVAL .
  9. 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.
    G10262495Courtesy of SUBARU OF AMERICA, INC.
  10. Install the battery. Ref. to STARTING/CHARGING SYSTEMS (H4DO)>BATTERY>INSTALLATION .
  11. Turn the ignition switch to ON.
  12. Depress the accelerator pedal to full throttle.
  13. 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 the standard value, check or adjust the pistons, valves and cylinders.

    Compression pressure: 

    At 200 - 300 r/min 

    Standard 

    1, 050 - 1, 400 kPa (11 - 14 kg/cm2 , 152 - 203 psi)

    Difference between cylinders 

    100 kPa (1 kg/cm2 , 14 psi) or less

  14. After inspection, install the related parts in the reverse order of removal.
    NOTE: When compression pressure is checked, the malfunction indicator light illuminates and DTCs may be stored in ECM. When the malfunction indicator light has illuminated, perform the Clear Memory Mode. Ref. to COMMON (DIAG)>CLEAR MEMORY>OPERATION .
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