Note. An assistant will be required to check the compression pressure.
Compression pressure measurement provides an overview of the current condition of internal engine components such as cylinder head gaskets, valve train components, pistons and piston rings. Analysis of the test results allows you to determine whether the engine needs a major overhaul, or it is enough to replace only the cylinder head gasket. The measurement is made using a compression gauge.
1. Warm up the engine to normal operating temperature (about 80 deg.) and mute it.
2. Make sure the battery is fully charged and relieve pressure in the power system (see Section Depressurizing the supply system).
Note. After relieving pressure, do not connect the fuel pump wiring until the end of the compression test.
3. Turn out All spark plug (see Section Replacing spark plugs) and connect a tachometer or turn on the Consult-II device in the appropriate mode.
4. Prepare a compression tester and screw its nozzle 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 so that it does not get stuck in the spark plug hole when removing.
5. Fully depress the gas pedal and, turning the engine with a starter, read and write down 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 measurement results with requirements Specifications.
Compression in a serviceable engine rises very quickly. A low reading after the first cycle, increasing with successive cycles, indicates worn piston rings. A low value after the first cycle that does not increase after the next cycle indicates valve leaks or a blown cylinder head gasket (Could also be a cracked head). The presence of soot 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 level of the minimum allowable and even lower, then to find out the reason, pour a teaspoon of engine oil into the cylinder through the candle hole and repeat the measurement.
If the addition of oil temporarily improves compression, the cause of the decrease is most likely piston, ring, or cylinder wear. If there is no increase in compression, then it can be assumed that the cause is valve leaks or a broken head gasket.
Low compression in two adjacent cylinders is almost certainly the 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 rest by more than 1 atm, moreover, 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. Don't forget to connect the fuel pump connector.