Note: An assistant will be required to check the compression pressure.
Measuring the compression pressure allows you to get a general idea of the current condition of such internal engine components as the cylinder head gasket, valve train components, pistons and piston rings. Analysis of the test results allows you to determine whether the engine needs a major overhaul or whether it is sufficient to replace only the cylinder head gasket. The measurement is performed using a compression tester.
1. Warm up the engine to normal operating temperature (about 80 degrees.) and muffle it.
2. Make sure that the battery is fully charged and relieve the pressure in the fuel system (see section Relieving pressure in the fuel system).
Note: After relieving pressure, do not connect the fuel pump wiring until the end of the compression pressure test.
3. Turn inside out all spark plugs (see section Replacing spark plugs) and connect the tachometer or turn on the Consult-II device in the appropriate mode.
4. Prepare a compression tester and screw its attachment into the spark plug hole of one of the cylinders.
Note: It is recommended to use a conical rubber nozzle with a diameter of no more than 20 mm to prevent it from getting stuck in the spark plug hole during removal.
5. Fully depress the gas pedal and, turning the engine with the starter, read and record the compression gauge readings when they stabilize.
Note: The measurement time should be as short as possible.
6. Repeat the procedures described in paragraphs 5 and 6 for the remaining engine cylinders.
7. Compare the measurement results with the requirements Specifications.
Compression in a healthy engine increases very quickly. A low value after the first cycle, increasing with subsequent cycles, indicates worn piston rings. A low value after the first cycle, not increasing after subsequent cycles, indicates leaks through the valves or a broken cylinder head gasket (the cause could also be a crack in the head). The presence of carbon deposits on the valve plates can lead to a decrease in compression.
The results obtained when measuring compression should be approximately the same for all cylinders. If the pressure in any cylinder is at the minimum permissible level or even lower, then to find out the reason, pour a teaspoon of engine oil into the cylinder through the spark plug hole and repeat the measurement.
If adding oil temporarily improves compression, the reason for its decrease is most likely wear of the piston, rings or cylinder. If there is no increase in compression, then it can be assumed that the cause is leaky valves or a broken head gasket.
Low compression in two adjacent cylinders is almost certainly a result of a blown head gasket. The presence of coolant in the combustion chambers or in the crankcase will confirm this assumption.
If the compression in one of the cylinders differs from the others by more than 1 atm, and the idle speed is unstable, then the reason may be excessive wear of the camshaft cam.
After checking, disconnect the compression tester and install the removed components. Do not forget to connect the fuel pump connector.