To obtain accurate test results, the engine must be warmed up to normal temperature and the battery fully charged.
1. Remove spark plugs.
2. Fully open the throttle.
3. Turn off the ignition by connecting the coil wire to ground. On injection engines, turn off the fuel pump (see subsection 5.1.4).
4. Insert the compression gauge into the spark plug hole of the 1st cylinder.
5. Turn on the starter and watch the pressure gauge. On a healthy engine, the pressure should build up quickly. Low pressure after the first piston stroke and a slow build-up on subsequent compression strokes indicates worn piston rings. If the pressure is low after the first piston stroke and does not increase on subsequent compression strokes, the cause is a leak in the valves or a leak in the gasket or cylinder head. Write down the highest compression value.
6. Repeat the procedure for the remaining cylinders.
7. Put some oil into the cylinders (10–15 cm3). If after the introduction of oil into the cylinder, the compression increased, then we can conclude that the piston rings are worn out. If the compression increases slightly, then the leak is through the valves, or the head gasket.
8. If the compression is equally low in only two adjacent cylinders, then the most likely cause is a burnt gasket between these cylinders.
9. If the compression value exceeds the norm, then the combustion chamber is covered with soot. In this case, the cylinder head must be removed and carbon deposits removed.
10. With a strong difference in compression in the cylinders, the car should be taken to a service station to check the tightness of the head and cylinder block by pressing.