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Home >> Nissan-Datsun >> 2004 >> Sentra SE-R >> Repair and Diagnosis >> External Pages >> Different car >> Section 1627 (Engine Mechanical - Sedan) >> Cylinder Head >> On-Vehicle Service >> Checking Compression Pressure

Checking Compression Pressure

WARNING: This page is about a different car, the 2003 Infiniti G35. However, it is still accessible from the selected car via links, so may be relevant.
  1. Warm up engine thoroughly. Then, stop it.
  2. Release fuel pressure. Refer to FUEL PRESSURE RELEASE TYPE 1 (TYPE 1) or FUEL PRESSURE RELEASE TYPE 2 (TYPE 2).
  3. Disconnect fuel pump fuse to avoid fuel injection during measurement.
  4. Remove engine cover with power tool.
  5. Remove ignition coil and spark plug from each cylinder. Refer to "IGNITION COIL " and "SPARK PLUG (PLATINUM-TIPPED TYPE) ".
  6. Connect engine tachometer (not required in use of CONSULT-II).
    Fig 1: Locating Fuel Pump Fuse
    G02151564Courtesy of NISSAN MOTOR CO., U.S.A.
  7. Install compression tester with adapter onto spark plug hole.
    Fig 2: Installing Compression Tester With Adapter
    G02151565Courtesy of NISSAN MOTOR CO., U.S.A.
    • Use compression gauge whose picking up end inserted to spark plug hole is smaller than 20 mm (0.79 in) in diameter. Otherwise, it may be caught by cylinder head during removal.
  8. With accelerator pedal fully depressed, turn ignition switch to "START" for cranking. When the gauge pointer stabilizes, read the compression pressure and engine RPM. Perform these steps to check each cylinder.
    Fig 3: Pressure Reference Chart
    G02151566Courtesy of NISSAN MOTOR CO., U.S.A.
    Fig 4: Measuring Diameter
    G02151567Courtesy of NISSAN MOTOR CO., U.S.A.
    CAUTION: Always use a fully changed battery to obtain specified engine speed.
    • If the engine speed is out of specified range, check battery liquid for proper gravity. Check engine speed again with normal battery gravity.
    • If compression pressure is below minimum value, check valve clearances and parts associated with combustion chamber (valve, valve seat, piston, piston ring, cylinder bore, cylinder head, cylinder head gasket). After the checking, measure compression pressure again.
    • If some cylinders have low compression pressure, pour small amount of engine oil into the spark plug hole of the cylinder to re-check it for compression.
      • If the added engine oil improves the compression, the piston rings may be worn out or damaged. Check the piston rings and replace if necessary.
      • If the compression pressure remains at low level despite the addition of engine oil, the valves may be malfunctioning. Check the valves for damage. Replace the valve or valve seat accordingly.
  9. After inspection is completed, install removed parts.
  10. Start engine, and confirm that engine runs smoothly.
  11. Perform trouble diagnosis. If DTC appears, erase it. Refer to TROUBLE DIAGNOSIS (TYPE 1) (TYPE 1) or TROUBLE DIAGNOSIS (TYPE 2) (TYPE 2).
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