1. Warm up the engine to operating temperature. In this case, the battery must be fully charged. Unscrew the spark plugs.
2. Disconnect electric wires from the distributor of ignition. On engines with a fuel injection system, remove the fuel pump relay, and on models with carburetors, disconnect the electrical connector from the fuel cutoff valve.
3. Install a compression tester in the hole of the candle of the first cylinder.
4. The assistant should press the accelerator pedal to the stop and turn the engine with the starter. After cranking the crankshaft one or two revolutions, the compression pressure should increase to maximum and then stabilize. Record your maximum score.
5. Check the rest of the cylinders in the same way.
6. The compression pressure in all cylinders must not differ by more than 1.5 bar. Note that the amount of compression should increase rapidly on a healthy engine. Low compression pressure on the first revolution of the crankshaft, followed by a gradual increase in pressure on subsequent revolutions of the crankshaft, indicates worn piston rings.
7. A low pressure value at the first revolution of the crankshaft, which increases slightly thereafter, indicates a valve leak, a blown cylinder head gasket, or a crack in the cylinder head. Worn valve stem ends can also result in low compression pressure.
8. If the pressure in one cylinder is low, then carry out the following test. Pour some engine oil through the spark plug hole into the cylinder and check the compression pressure.
9. If adding oil to the cylinder increases the compression pressure, this indicates that the cylinder or piston rings are worn.
10. Low pressure in two adjacent cylinders indicates a burnt gasket between the cylinders.
11. If the pressure in one cylinder is less than 20% than in the others, and the engine is unstable at idle, this indicates a worn camshaft cam.
12. If the compression pressure is too high, this indicates that the combustion chamber is covered with a thick layer of soot.
13. After this check, screw in the spark plugs, connect the high voltage wires and install the fuel pump relay.