Compression Check: Testing and Inspection

COMPRESSION PRESSURE

On-Vehicle Service


CHECKING COMPRESSION PRESSURE

1.Run the engine until it reaches normal operating temperature.
2.Turn the ignition switch to OFF.
3.Release fuel pressure and leave the fuel pump electrically disconnected.
Refer to "Work Procedure" Testing and Inspection.
4.Remove all six spark plugs.
Refer to "Removal and Installation" Removal and Installation.





5.Attach a compression tester to No. 1 cylinder.
6.Depress accelerator pedal fully to keep the electric throttle control actuator butterfly-valve wide open to maximize air intake flow.
7.Crank the engine and record the highest gauge indication.

CAUTION:
Always use a fully charged battery to obtain specified engine speed.
8.Repeat the test for each cylinder (steps 5 - 7).
Unit: kPa (kg/cm, psi) /rpm





- 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 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 respectively low compression pressure and their compression remains low even after the addition of engine oil, cylinder head gaskets may be leaking, or a valve in adjacent cylinders may be damaged. Inspect and repair as required.
- 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 the checking, measure the compression pressure again.
9.Installation of the remaining components is in the reverse order of removal.
Revision: March 20122013 Infiniti JX