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Home >> Nissan-Datsun >> 2021 >> Sentra S >> Repair and Diagnosis (Single Page) >> Engine Mechanical >> Engine Mechanical >> Basic Inspection >> Compression Pressure >> Inspection
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Compression Pressure: Inspection

  1. Warm up engine to full operating temperature. Stop engine.
  2. Release the fuel pressure. Refer to Work Procedure .
  3. Remove the fuel pump fuse from IPDM E/R to avoid fuel injection during measurement.
  4. Remove ignition coil and spark plug from each cylinder. Refer to Removal and Installation .
  5. Connect engine tachometer (not required when using CONSULT).
  6. Install suitable tool (A) with suitable tool (B) onto spark plug hole.
    GNSILL0259684-684Courtesy of NISSAN NORTH AMERICA, INC.
    • Use compression tester whose end (rubber portion) is smaller than 20 mm (0.79 in) in diameter (A). Otherwise, it may be caught by cylinder head during removal.
      GNSAWBIA3080Z-080Courtesy of NISSAN NORTH AMERICA, INC.
  7. With accelerator pedal fully depressed, crank engine. When the gauge pointer stabilizes, read the compression pressure and the engine RPM. Perform these steps to check each cylinder.

    Compression pressure

    : Refer to General Specification .
    CAUTION: Always use a fully charged battery to obtain the specified engine speed.
    • If the engine speed is out of the specified range, check the battery. Check the engine speed again with a fully charged battery.
    • If some cylinder has low compression pressure, pour small amount of engine oil into the spark plug hole of the cylinder to recheck it for compression.
      • If the added engine oil improves the compression, piston rings may be worn out or damaged. Check piston rings and replace if necessary.
      • If the compression pressure remains at low level despite the addition of engine oil, valves may be malfunctioning. Check valves for damage. Replace valve or valve seat accordingly.
    • If two adjacent cylinders have respectively low compression pressure and their compression remains low even after the addition of engine oil, cylinder head gaskets are leaking. In such a case, replace cylinder head gaskets.
    • 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.
  8. After inspection is completed, installation is in the reverse order of removal.
  9. Start the engine, and check that the engine runs smoothly.
  10. Perform trouble diagnosis. If DTC appears, erase it. Refer to Work Procedure .
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