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Toyota Supra JZA80

Compression

If there is lack of power, excessive oil consumption or poor fuel economy, measure the compression pressure.
  1. Warm up and stop engine
    Allow the engine to warm up to normal operating temperature.
  2. Disconnect distributor connector
  3. Disconnect high tension codes from spark plugs
  4. Remove spark plugs
  5. Check cylinder compression
    1. Insert a compression tester into the spark plug hole.
    2. While cranking the engine, measure the compression pressure.
      Always use a fully charged battery to obtain engine revolutions of 250 rpm or more.
    3. Repeat steps (a) through (b) for each cylinder.
      This measurement must be done in as short a time as possible.
      Compression:
      1,275 kPa (13.0 kgf/cm 2 , 185 psi) or more
      Minimum pressure:
      1,079 kPa (11.0 kgf/cm 2 , 156 psi)
      Difference between each cylinder:
      98 kPa (1.0 kgf/cm 2 , 14 psi) or less
    4. 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 (a) through (b) for the cylinder with low compression.
      • If adding oil helps the compression, it is likely that the piston rings and/or cylinder bore are probably worn or damaged.
      • If pressure stays low, a valve may be sticking or seating improper, or there may be leakage past the gasket.
  6. Reinstall spark plugs
  7. Reconnect high-tension coeds to spark plugs (See page IG-10 )
  8. Reconnect distributor connector
This guide is based on the book edition Toyota (RM502U, 1997)

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