Compression Inspection

WARNING: This page is about a different car, the 2004 Mazda RX-8. However, it is still accessible from the selected car via links, so may be relevant.

WARNING:

Hot engines can cause severe burns. Be careful not to burn yourself during removal/installation of each component.
Fuel vapor is hazardous. It can very easily ignite, causing serious injury and damage. Always keep sparks and flames away from fuel.

Remove the engine cover. (See ENGINE COVER REMOVAL/INSTALLATION .)
Verify that the battery is fully charged.
Warm up the engine.
To decrease the exhaust system temperature, stop the engine and leave it as it is for approx. 10 min.
Remove the trailing or leading side spark plug of the front and rear rotors. (See SPARK PLUG REMOVAL/INSTALLATION .)
Disconnect the eccentric shaft position sensor connector. (See ECCENTRIC SHAFT POSITION SENSOR REMOVAL/INSTALLATION .)
CAUTION:
- To cut the fuel injection and ignition, make sure the eccentric shaft position sensor connector is disconnected.
Measure the compression pressure using one of the following procedures:
1. Install the SST (49 F018 901) to the trailing or leading side plug hole of the rotor housing.
2. Set the SST (49 F018 9A0B) as shown in the figure. See Fig 1.
  
  Fig 1: Measuring Compression Pressure
  Courtesy of MAZDA MOTORS CORP.
  - When using the WDS or equivalent, set the WDS or equivalent to the SST (49 F018 901, 49 F018 904) as shown in the figure.
3. Depress the accelerator pedal fully and crank for 5-10 seconds.
4. Read the compression and engine speed.
  
  Fig 2: Measuring Compression Pressure Using WDS
  Courtesy of MAZDA MOTORS CORP.
  
  Compression pressure
  - Standard: 830 kPa {8.5 kgf.cm ² , 120 psi} [250 RPM]
  - Minimum: 680 kPa {6.9 kgf.cm ² , 98.6 psi} [250 RPM]
  - Standard difference in chambers: Within 150 kPa {1.5 kgf.cm ² , 21.8psi}
  - Standard difference in rotors: Within 100 kPa {1.0 kgf.cm ² , 14.5 psi}
5. Perform the same procedure for the other rotor housing.
6. If the compression is at the minimum or less, or the difference in the chambers and difference in the rotors exceed the specifications, replace or overhaul.
  CAUTION:
  - If the engine speed when measuring compression differs from the standard, adjust according to the graph.
Install the spark plugs. (See SPARK PLUG REMOVAL/INSTALLATION .)
Connect the eccentric shaft position sensor connector. (See ECCENTRIC SHAFT POSITION SENSOR REMOVAL/INSTALLATION .)
Install the engine cover. (See ENGINE COVER REMOVAL/INSTALLATION .)

Fig 3: Compression Pressure/Cranking Speed Graph
Courtesy of MAZDA MOTORS CORP.