Note. The engine must be warmed up to normal operating temperature and the battery fully charged.
Gas engine
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 Vehicle settings and routine maintenance).
3. Lock the throttle in the fully open position.
4. Turn off the ignition system, To do this, remove the IGN fuse from the mounting block (see chapter Engine electrical equipment). Also disconnect the electrical wiring from the fuel pump (see chapter Power supply and exhaust systems).
5. Install the compression gauge in the spark plug hole of the first cylinder.
6. Crank the engine through at least seven compression 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 compression gauge reading.
7. Repeat the procedure for the remaining engine cylinders. Compare results with regulatory requirements (see Specifications).
8. If the measurement is too low, fill each of the cylinders through the spark plug hole with a little impellent oil (two to three teaspoons) and recheck.
9. 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.
10. 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.
11. 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 drive cams of the corresponding valves on the camshaft should be assessed.
12. 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.
13. 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.
14. Reinstall the fuses and drive the car for a short trip to restore the settings recorded in the processor's memory.
Diesel engine
The measurement of compression pressure in the cylinders of a diesel engine is carried out according to the same principle as on a gasoline engine, but the pressure gauge is installed instead of the fuel injector. Removal of nozzles is described in the Chapter Power supply and exhaust systems.
Note. When checking, the remaining 5 injectors must be installed.