Note. The engine must be warmed up to normal operating temperature and the battery fully charged.
1. 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.
2. Remove all spark plugs from the engine (see chapter Current service).
3. Lock the throttle in the fully open position.
4. Immobilize the power system by removing the PGM-FI main relay fuse (see chapter Power and exhaust systems).
5. Also turn off the ignition system by disconnecting the distributor primary circuit connectors (see chapter Engine electrical equipment).
6. Install the compression gauge in the spark plug hole of the first cylinder (see accompanying illustration).
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 cranking, this can be considered as evidence of valve leaks or a leak in the cylinder head gasket (the possibility of cracks in the head is also not excluded). Record the maximum pressure gauge reading.
8. Repeat the procedure for the remaining engine cylinders. Compare results with regulatory requirements (see Specifications).
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 of the plates.
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 exhaust valve drive cam on the camshaft should be assessed.
13. An unusual increase in compression pressure is usually the result of carbon deposits 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 compression pressure, as well as in case of a strong violation of the uniformity of its distribution between the cylinders, it will be useful to test the engine in a car service workshop. This test will pinpoint the exact location of the pressure leak and assess its severity.