Compression Inspection

WARNING:

Hot engines and engine 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 [BP, BP WITH TC] .)

Verify that the battery is fully charged.
Charge it again if necessary. (See BATTERY RECHARGING .)
Warm up the engine to the normal operating temperature.
Stop the engine and allow it to cool off for about 10 min.
Perform "Fuel Line Safety Procedure". (See BEFORE SERVICE PRECAUTION [BP, BP WITH TC] .)
Leave the fuel pump relay removed.
Remove the spark plugs. (See SPARK PLUG REMOVAL/INSTALLATION .)
Disconnect the ignition coil connector.
Connect a compression gauge into the No. 1 spark plug hole.
Fully depress the accelerator pedal and crank the engine.
Record the maximum gauge reading.
Inspect each cylinder as above.
- If the compression in one or more cylinders is low or the compression difference between cylinders exceeds the maximum, pour a small amount of clean engine oil into the cylinder and inspect the compression again.
  - If the compression increases, the piston, the piston rings, or cylinder wall 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 the compression in adjacent cylinders stays low, the cylinder head gasket may be damaged or the cylinder head is distorted and overhaul is required.
Compression

Fig 1: Compression Specification Table
Courtesy of MAZDA MOTORS CORP.
Disconnect the compression gauge.
Connect the ignition coil connector.
Install the fuel pump relay.
Install the spark plugs. (See SPARK PLUG REMOVAL/INSTALLATION .)