2. The engine must be warmed up to normal operating temperature, the battery must be fully charged, all injectors must be removed.
3. Shut off the fuel system by disconnecting the wiring from the fuel cutoff valve on the fuel pump.
4. Install a compression gauge in the injector hole of cylinder No. 1.
5. Turn the engine over with a starter; after one or two revolutions, the compression pressure should increase to a maximum value and then stabilize. Write down the maximum compression value.
6. Repeat the test on the remaining cylinders.
7. 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 and then a gradual increase in pressure on subsequent revolutions indicates worn piston rings. Low compression on the first stroke that does not increase during subsequent revolutions indicates leaking valves or a blown head gasket (also the reason may be in a split head). Carbon deposits on the backs of the valve heads can also be the cause of low compression.
8. If the compression value is below 17 bar, the engine can be considered in need of repair. Consult an 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, this indicates that the cylinder bore or piston is worn. If there is no increase in compression, leak through the valves or a blown cylinder head gasket.
11. Low compression in two adjacent cylinders most likely due to breakdown of the gasket between them; the presence of coolant liquid in the engine oil will confirm this.
12. If the compression in one cylinder is about 20% lower than in the others and the engine is rough at idle, the cause is probably worn camshaft lobes.
13. If the compression is unusually high, the combustion chambers are probably covered with soot. If so, the cylinder head needs to be removed and cleaned.
14. At the end of the test, install the injectors, connect the wiring to the fuel cut-off valve winding on the high pressure fuel pump.
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