2. The engine must be warmed up to normal operating temperature, the battery must be fully charged, all injectors must be removed.
3. Disconnect the fuel system by disconnecting the wiring from the fuel shut-off valve at the fuel pump.
4. Install the compression gauge into the injector hole of cylinder No.1.
5. Turn the engine over with the starter; after one or two revolutions, the compression pressure should increase to the maximum value and then stabilize. Record the maximum compression value.
6. Repeat the test on the remaining cylinders.
7. The compression values on all cylinders should be very close; a difference of more than 2 bar between any two cylinders indicates damage. Note that in a healthy engine, compression should build up quickly; low compression on the first stroke, then a gradual increase in pressure over subsequent revolutions indicates worn piston rings. Low compression on the first stroke that does not increase over subsequent revolutions indicates leaking valves or a blown head gasket (also the reason may be a split head). Carbon deposits on the backs of the valve heads can also be a cause of low compression.
8. If the compression value is below 17 bar, the engine can be considered in need of repair. Consult your Opel dealer or other specialist.
9. If the pressure in any cylinder is low, perform the following test to isolate the cause. Pour clean oil into the cylinder through the spark plug hole and repeat the test.
10. If adding oil temporarily increases compression, it indicates that the cylinder bore or piston is worn. If there is no increase in compression, there is a valve leak or a blown head gasket.
11. Low compression in two adjacent cylinders is most likely due to a blown gasket between them; the presence of coolant in the engine oil will confirm this.
12. If the compression in one cylinder is approximately 20% lower than in the others and the engine runs rough at idle, the cause is probably worn camshaft lobes.
13. If the compression is unusually high, the combustion chambers are probably covered with carbon deposits. If so, the cylinder head will need to be removed and cleaned.
14. At the end of the test, install the injectors, connect the wiring to the winding of the fuel cut-off valve on the high-pressure fuel pump.
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