Compression Inspection

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". (Refer to BEFORE SERVICE PRECAUTION .)

Verify that the battery is fully charged. (Refer to BATTERY INSPECTION .)
- Recharge it if necessary. (Refer to BATTERY RECHARGING .)
Connect the M-MDS to the DLC-2.
Warm up the engine to the normal operating temperature.
Display the following PIDs using the M-MDS data monitor function. (Refer to PCM INSPECTION .)
- RPM (engine speed)
Perform "Fuel Line Safety Procedures ". (Refer to BEFORE SERVICE PRECAUTION .)
Remove the following parts:
1. Plug hole plate (Refer to PLUG HOLE PLATE REMOVAL/INSTALLATION .)
2. Fuel injector relay
3. Ignition coil/ion sensors (Refer to IGNITION COIL/ION SENSOR REMOVAL/INSTALLATION .)
4. Spark plugs (Refer to SPARK PLUG REMOVAL/INSTALLATION .)
Measure the compression pressure using the following procedure.
1. Install the compression gauge to the spark plug hole.
2. Fully depress the accelerator pedal.
  NOTE:
  - The cranking method is as follows.
    
    When the ignition switch is pressed with the brake pedal depressed, cranking starts.
    
    When the ignition switch is pressed during cranking, cranking stops.
3. Crank the engine and measure the following values simultaneously.
  - Compression pressure
  - Engine speed
  Compression pressure
  
  Fig 1: Engine Speed And Compression Pressure Value Graph
  Courtesy of MAZDA
  - Standard: Refer to the graph.
  - Minimum: Refer to the graph.
  - Maximum difference between cylinders: 148 kPa {1.51 kgf/cm² , 21.5 psi} [250 rpm]
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. Spark plugs (Refer to SPARK PLUG REMOVAL/INSTALLATION .)
2. Ignition coil/ion sensors (Refer to IGNITION COIL/ION SENSOR REMOVAL/INSTALLATION .)
3. Fuel injector relay
4. Plug hole plate (Refer to PLUG HOLE PLATE REMOVAL/INSTALLATION .)