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Checking Compression Pressure

WARNING: This page is about a different car, the 2004 Infiniti M45 and 2003 Infiniti M45. However, it is still accessible from the selected car via links, so may be relevant.
  1. Warm up engine thoroughly. Then, stop it.
  2. Remove engine cover (with power tool). Refer to REMOVAL AND INSTALLATION .
  3. Release fuel pressure.
    1. Remove fuel pump fuse, and start engine. Refer to FUEL PRESSURE RELEASE for fuel pump fuse location.
    2. After engine stalls, crank it two or three times to release all fuel pressure.
      • Let fuel pump fuse removed until the end of step 7.
  4. Remove ignition coil and spark plug from each cylinder. Refer to REMOVAL AND INSTALLATION  and SPARK PLUG (PLATINUM-TIPPED TYPE) .
  5. Connect engine tachometer (not required in use of CONSULT-II).
  6. Install compression gauge with adapter (SST or commercial service tool) onto spark plug hole.
    • Use compression gauge adapter (SST) which is required on No. 7 and No. 8 cylinders.
      Fig 1: Checking Compression Pressure
      G00796941Courtesy of NISSAN MOTOR CO., U.S.A.
    • Use the compression gauge adapter (if SST is not used) which 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.
    Fig 2: Using Compression Adapter Required On No. 7 & No. 8
    G00796942Courtesy of NISSAN MOTOR CO., U.S.A.
  7. 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.

    Compression pressure 

    Fig 3: Reviewing Compression Pressure Information
    G00796943Courtesy of NISSAN MOTOR CO., U.S.A.
    CAUTION: Always use a fully charged 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.
    • If two adjacent cylinders have respectively low compression pressure and their compression remains low even after the addition of engine oil, the gaskets are leaking. In such a case, replace the cylinder head gaskets.
  8. Install removed parts in the reverse order of removal.
  9. Start engine, and confirm that engine runs smoothly.
  10. Perform trouble diagnosis. If DTC appears, erase it. Refer to TROUBLE DIAGNOSIS .
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