Attention! Important conditions for correct readings when checking compression in cylinders are the serviceability of the starter and its electrical circuits, as well as a full charge of the battery.
The car's cylinder compression is checked with a special device - a compression meter, which is now freely available in large auto parts stores and on the automotive market.
1. Before measuring the compression in the cylinders, check and, if necessary, adjust the clearances in the valve mechanism (see "Adjusting valve clearances").
2. Start the car engine and warm it up to operating temperature.
3. Reduce the pressure in the fuel system (see "Reduced fuel pressure in the engine fuel system"). After the pressure in the engine fuel system has dropped, do not replace the fuel pump fuse to disable the fuel pump.
4. Remove the high-voltage wire tips from the spark plugs...
5. ...and remove all spark plugs from the engine.
6. Disconnect the low voltage wire harness connector from the ignition coil, thereby disabling the vehicle's ignition system.
7. Screw the compression gauge into the spark plug hole of the cylinder being tested.
8. Press the gas pedal all the way down to fully open the throttle valve.
9. Turn the key in the ignition switch and turn on the starter and turn the engine crankshaft until the pressure in the cylinder stops increasing. This corresponds to approximately four compression strokes. To obtain correct compression tester readings, the crankshaft must rotate at 180-200 rpm or higher, but not more than 350 rpm.
10. After recording the compression gauge readings, set its arrow to zero by pressing the air release valve.
11. Repeat compression measurement 7-10 for the remaining cylinders. Compression should be no lower than 1.0 MPa and should not differ in different cylinders by more than 0.1 MPa. Reduced compression in individual cylinders may occur as a result of loose valve seating, damage to the cylinder head gasket, or broken or burnt piston rings. Low compression in all cylinders indicates wear of the piston rings.
12. To determine the reasons for insufficient compression, pour about 20 cc of clean motor oil into the cylinder with low compression and measure the compression again. If the compression gauge readings have increased, the piston rings are most likely faulty. If the compression value remains unchanged, it means that the valve plates are not tightly seated in the seats or the cylinder head gasket is damaged.