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Home >> Kia >> 2017 >> Optima Plug-In Hybrid EX >> Repair and Diagnosis >> Engine Mechanical >> Mechanical >> Engine Mechanical System - General Information (PHEV) >> Repair Procedures >> Compression Pressure Inspection

Compression Pressure Inspection

NOTE: If the there is lack of power, excessive oil consumption or poor fuel economy, measure the compression pressure.
  1. Warm up and stop the engine.

    Allow the engine to warm up to normal operating temperature.

  2. Disconnect the ignition coil connectors (A).
    G12346930Courtesy of KIA MOTORS AMERICA, INC.
  3. Remove spark plugs.

    (Refer to Engine Electrical System - "SPARK PLUG ")

  4. Check cylinder compression pressure.
    1. Insert a compression gauge into the spark plug hole. If possible, place the gauge where it can be seen from inside the vehicle.
      G12346931Courtesy of KIA MOTORS AMERICA, INC.
    2. Attach the KDS/GDS
      • Connect the cable of KDS/GDS to the data link connector.
      • Select the vehicle model and then the HCU system.
      • Select the "Engine On Test". See the screens below.
    3. While cranking the engine, measure the compression pressure.
      • With the Brake pedal depressed, press the Start/Stop Button (SSB) one time.
      • If the engine cranks, let it crank about 8 to 10 cycles (until the gauge readings stabilizes) then press the SSB one time to stop the engine from cranking.
      • If the engine does not crank on its own when the SSB is pressed, the KDS/GDS should be used to crank the engine. While in the "Engine On Test" follow the instruction on the screen.
      • The "Engine On Test" will start the engine cranking. After the compression readings stabilize (8-10 cycles), press the SSB one time to stop the cranking.
      G12346932Courtesy of KIA MOTORS AMERICA, INC.
      G12346933Courtesy of KIA MOTORS AMERICA, INC.
      G12346934Courtesy of KIA MOTORS AMERICA, INC.
      G12346935Courtesy of KIA MOTORS AMERICA, INC.
    4. Repeat steps (1) through (3) for each cylinder.
      NOTE: Be sure ignition is in the OFF mode between each cylinder test.
      This measurement must be done while the engine is still near operating temperature.

      Compression pressure: 

      981kPa (10.0kgf/cm2 , 142psi)/300 - 350 RPM

      Minimum pressure: 

      834kPa (8.5kgf/cm2 , 121psi)/300 - 350 RPM

      Difference between each cylinder: 

      100kPa (1.0kgf/cm2 , 15psi) or less

    5. If the cylinder compression in 1 or more cylinders is low, pour a small amount of engine oil into the cylinder through the spark plug hole and repeat steps (1) through (3) for cylinders with low compression.
      • If adding oil helps the compression, it is likely that the piston rings and/or cylinder bore are worn or damaged.
      • If pressure stays low, a valve may be sticking or seating is improper, or there may be leakage past the gasket.
  5. Reinstall spark plugs.

    Tightening torque: 

    14.7 - 24.5 N.m (1.5 - 2.5 kgf.m, 10.8 - 18.1 lb.ft)

  6. Install ignition coils.

    Tightening torque: 

    9.8 - 11.8 N.m (1.0 - 1.2 kgf.m, 7.2 - 8.7 lb.ft)

  7. Connect the injector connectors and ignition coil connectors.
  8. Some DTC's may exist after the inspection test and may need to be manually cleared with KDS/GDS.
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