2. To obtain accurate test results, the engine must be warm, the battery must be fully charged, and the spark plugs must be removed (see Chapter 1). You will also need the help of another person.
3. Completely turn off the ignition and fuel system by disconnecting the connector from the ignition unit and removing the fuel pump relay from the panel in the engine compartment (Chapter 4A).
4. Insert the compression gauge into the spark plug hole of cylinder 1 (see photo). It is preferable to use a gauge with a threaded tip.
5. Ask an assistant to fully depress the throttle pedal and engage the starter for a few seconds. After the first two crankshaft revolutions, the pressure in the gauge should increase to maximum. Record the maximum reading on the gauge.
6. Repeat the measurements for the remaining cylinders, record the meter readings.
7. The compression readings in the cylinders should be almost the same. If the difference in compression exceeds the norm, the engine is faulty. On a serviceable engine, the pressure should increase quickly. Low pressure after the first stroke of the piston and a slow increase during subsequent compression strokes indicates wear of the piston rings. If the pressure is low after the first stroke of the piston and does not increase during subsequent compression strokes, the cause is a leak in the valves or a leak in the cylinder head gasket (cracks in the cylinder head may also be the cause). A decrease in compression can also be caused by carbon deposits on the valve heads.
8. If the pressure in each cylinder is at or below the lower limit, then inject some engine oil into the cylinder through the spark plug hole (about a full teaspoon), then repeat the tests.
9. If the compression increases after adding oil to the cylinder, then we can make a clear conclusion that the cylinder walls and pistons are worn out. If the compression increases slightly or does not increase at all, then the leak is caused by burnt valves or a leak in the cylinder head gasket.
10. If the compression is equally low only in two adjacent cylinders, then the most likely cause is a burnt gasket between these cylinders. An additional sign is the presence of traces of coolant in the oil.
11. If the compression in one of the cylinders is 20% lower than in the others and the engine runs unstably at idle, then the cause is wear of the camshaft cam of this cylinder.
12. If the compression value is significantly higher than normal, then the combustion chamber is covered with carbon deposits. In this case, the cylinder head must be removed and the carbon removed.
13. After completing the measurements, screw in the spark plugs and connect the connector to the ignition unit.
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