Note. The engine must be warmed up to normal operating temperature and the battery fully charged.
2. Start by cleaning the candle niches (blow them with compressed air, the source of which in this case is perfect for an ordinary bicycle pump). The main objective is to prevent debris from entering the cylinders during measurements.
3. Relieve pressure in the supply system (see chapter Power and exhaust systems). The fuel pump must be off during this procedure.
4. Remove all spark plugs from the engine (see chapter Settings and ongoing maintenance). Lock the throttle in the fully open position.
5. On models equipped with an ignition distributor, disconnect the central (coil wire) and ground it to the engine block. On models without a distributor, disconnect the electrical wiring from each of the ignition coils.
6. Install the compression tester in the spark plug hole of the first cylinder.
7. Turn the engine over at least seven strokes and read the gauge. On a healthy engine, the pressure should build up fairly quickly. Low pressure on the first stroke, accompanied by a gradual increase in subsequent strokes, indicates wear on the piston rings. If the pressure does not rise with further rotation of the shaft, this can be regarded as evidence of valve leaks or a leak in the cylinder head gasket (the possibility of cracks in the head is also not excluded). The accumulation of deposits on the working facets of the valve plates can also lead to a decrease in compression pressure. Record the maximum pressure gauge reading.
8. Repeat the procedure for the remaining engine cylinders. Compare results with regulatory requirements (see specs).
9. If the measurement is too low, pour a little engine oil into each of the cylinders through the spark plug hole (two to three teaspoons) and recheck.
10. If the addition of oil leads to an increase in pressure, this indicates wear on the piston rings. If the compression does not increase, the cause of the decrease is valve leaks or a leaking head gasket. Valve leaks can be associated with burnout of their seats, or deformation / burnout or mechanical damage to the working chamfers.
11. If the compression pressure is equally low in two adjacent cylinders, then with a high degree of probability we can talk about a violation of the integrity of the head gasket within its jumper between these cylinders. The presence of coolant in the engine oil will confirm this assumption.
12. If the pressure in one of the cylinders is about 20% lower than in the others and this is accompanied by a violation of the stability of the idle speed, the degree of wear of the corresponding valve drive cams on the camshaft should be assessed.
13. An unusual increase in compression pressure is usually the result of excessive carbon formation in the combustion chambers. In this case, the cylinder head must be removed in order to carry out decarbonization.
14. In case of excessively low measurement results, as well as in the event of a violation of the uniform distribution of pressure between the cylinders, it will be useful to test the engine for leaks in a car service workshop. This check will pinpoint the source of the leak and assess its severity.