Compression Check: Testing and Inspection

Compression Pressure

Checking Compression Pressure

1) Warm up engine thoroughly.
2) Release fuel pressure. Refer to [Fuel Pressure Check: VQ40DE] Testing and Inspection.
3) Disconnect fuel pump fuse to avoid fuel injection during measurement.





4) Remove intake manifold collector. Refer to [Intake Manifold Collector: Removal and Installation] Intake Manifold Collector Removal and Installation.
5) Remove spark plug from each cylinder. Refer to [Spark Plug: Removal and Installation] Removal and Installation.
6) Connect engine tachometer (not required in use of SDT).
7) Install compression tester with adapter onto spark plug hole.





- Use compression gauge whose pick up end inserted to spark plug hole is smaller than 20 mm (0.79 in) in diameter. Otherwise, it may be caught by cylinder head during removal.





8) Turn ignition switch to "START" for cranking. When the gauge pointer stabilizes, read the compression pressure and engine rpm. Perform these steps to check each cylinder.
Compression pressure:

Unit: kPa (kg/cm2, psi) /rpm






CAUTION:
Always use a fully charged battery to obtain specified engine speed.

- If the engine speed is out of the specified range check the battery and recharge as necessary. Check the engine speed again with the battery properly charged.
- If some cylinders have low compression pressure, pour a small amount of engine oil into the spark plug hole of the cylinder to re-check it for compression.
- If the added engine oil improves the compression, piston rings may be worn out or damaged. Check the piston rings and replace if necessary
- If the compression pressure remains at a low level despite the addition of engine oil, the valves may be malfunctioning. Check the valves for damage. Replace the valve or valve seat accordingly.
- If two adjacent cylinders have low compression pressure and their compression remains low even after the addition of engine oil, cylinder head gaskets may be leaking.
- If the compression pressure is below the minimum value, check the valve clearances and parts associated with the combustion chamber (valve, valve seat, piston, piston ring, cylinder bore, cylinder head, cylinder head gasket). After repairing as necessary, measure the compression pressure again.
9) Install the components in the reverse order of removal.
10) Start the engine, and confirm that it runs smoothly.
11) Perform trouble diagnosis. If DTC appears, erase it.