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Compression Inspection

WARNING: This page is about a different car, the 2004 Mazda MPV. However, it is still accessible from the selected car via links, so may be relevant.
WARNING:
  • When the engine and the oil are hot, they can badly burn. Turn off the engine and wait until they are cool.
  1. Verify that the battery is fully charged.
  2. Warm up the engine to the normal operating temperature.
  3. Perform "Fuel Line Safety Procedure". Leave the fuel pump relay removed. (See FUEL LINE SAFETY PROCEDURE .)
  4. Remove the ignition coils. (See IGNITION COIL REMOVAL/INSTALLATION .)
  5. Remove the spark plugs.
  6. Install the compression gauge into the spark plug hole.
    Fig 1: Installing Compression Gauge Into Spark Plug Hole
    G00993491Courtesy of MAZDA MOTORS CORP.
  7. Crank the engine a minimum of five compression strokes and record the highest reading. Note the approximate number of compression strokes required to obtain the highest reading.
  8. Repeat the test on each cylinder, cranking the engine approximately the same number of compression strokes.
  9. The indicated compression pressures are considered within specification if the lowest reading cylinder is within 75% of the highest reading  .
    • If the compression in one or more cylinder is low or the compression difference between cylinders exceeds the maximum, pour a small amount of clean engine oil into the cylinder and recheck the compression.
    • If the compression increases, the piston, the piston rings, or cylinder wall may be worn may be worn and overhaul is required.
    • If the compression stays low, a valve may be stuck or improperly seated and overhaul is required.
    • If two adjacent cylinders indicate low compression pressures and squirting oil on piston does not increase compression the head gasket may be leaking between cylinders. Engine oil and/or coolant in the cylinders could result from this condition.
  10. Remove the compression gauge.
  11. Install the spark plugs.

    Tightening Torque 

    9-20 N.m {91-204 kgf. cm, 79-177 in. lbf} 

  12. Install the ignition coils. (See IGNITION COIL REMOVAL/INSTALLATION .)
  13. Install the fuel pump relay.
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