Compression Inspection

WARNING: This page is about a different car, the 2014 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.

WARNING:

Hot engines and oil 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.
Fuel line spills and leakage are dangerous. Fuel can ignite and cause serious injuries or death and damage. Fuel can also irritate skin and eyes. To prevent this, always complete the "Fuel Line Safety Procedure". (See BEFORE SERVICE PRECAUTION .)

Verify that the battery is fully charged. (See BATTERY INSPECTION [SKYACTIV-G 2.5] .)
- Recharge it if necessary. (See BATTERY RECHARGING [SKYACTIV-G 2.5] .)
Warm up the engine to the normal operating temperature.
Perform "Fuel Line Safety Procedures". (See BEFORE SERVICE PRECAUTION .)
Remove the following parts.
1. Plug hole plate. (See PLUG HOLE PLATE REMOVAL/INSTALLATION .)
2. Ignition coil/ion sensors. (See IGNITION COIL/ION SENSOR REMOVAL/INSTALLATION .)
3. Spark plugs. (See SPARK PLUG REMOVAL/INSTALLATION .)
4. Fuel pump relay
5. Fuel injector relay
Measure the compression pressure using the following procedure.
1. Press a compression gauge into the spark plug hole.
2. Fully depress the accelerator pedal.
3. Crank the engine and measure the compression pressure.
  Compression
  
  Standard: 954 kPa (9.73 kgf/cm ² , 138 psi} [300 rpm]
  
  Minimum: 763 kPa (7.78 kgf/cm ² , 111 psi} [300 rpm]
  
  Maximum difference between cylinders: 161 kPa {1.64 kgf/cm ² , 23.4 psi} [300 rpm]
  NOTE:
  - Because the SKYACTIV-G 2.5 retards the intake valve closing timing, compression pressure is low.
  Fig 1: Measuring Compression Pressure
  Courtesy of MAZDA MOTORS CORP.
4. Perform Steps ( 1) to ( 3) for all cylinders.
5. If the measured value is the threshold or less, or if there is a cylinder which exceeds the specified maximum difference between cylinders, add a small amount of engine oil through the spark plug hole and perform Steps ( 1) to ( 3).
  - If the pressure increases by adding the engine oil, the piston ring or the cylinder surface is worn, or they are damaged. Perform overhaul servicing.
  - If the pressure does not increase, valve seizure, valve attachment malfunction, or pressure leakage from the cylinder head gasket might be occurring. Perform overhaul servicing.
6. If the measured value is high, it is possible that there is an error in the electric variable valve timing system.
Remove the compression gauge.
Install the following parts.
1. Fuel injector relay
2. Fuel pump relay
3. Spark plugs. (See SPARK PLUG REMOVAL/INSTALLATION .)
4. Ignition coil/ion sensors. (See IGNITION COIL/ION SENSOR REMOVAL/INSTALLATION .)
5. Plug hole plate. (See PLUG HOLE PLATE REMOVAL/INSTALLATION .)