2. Engine warmed up to normal operating temperature, battery fully charged, all spark plugs removed (see chapter Current service). You will also need the help of an assistant.
3. De-energize the ignition system by disconnecting the BB wire of the ignition coil from the distributor cap and grounding it to the cylinder block (use jumper wire). On models without an ignition distributor, disconnect the electrical connector at the ignition coil assembly at the front of the cylinder head.
4. To prevent damage to the catalytic converter, depressurize the injection system and shut off the power system by removing the fuel pump relay (see chapter Supply system).
5. Connect the compression tester to the spark plug hole of the 1st cylinder (it is preferable to use a meter with a threaded tip).
6. Ask the assistant to depress the accelerator pedal all the way and turn the engine over with the starter. After the first two turns of the crankshaft, the instrument reading should reach its maximum value. Record the result.
7. Repeat the measurement for the remaining cylinders, record the results.
8. The pressure in all cylinders should be practically the same in the range from 11 to 15 bar. A difference in readings greater than 1.5 bar should be considered as a sign of a violation. It is also unacceptable to lower the compression pressure below 10 bar.
9. Remember that the pressure in a serviceable engine should rise quickly enough. A low reading on the first stroke with a gradual increase in subsequent strokes indicates worn piston rings.
10. If the pressure does not rise at all, you should check the tightness of the closing of the valves and the condition of the cylinder head gasket (the possibility of cracks in the head is also not excluded). The accumulation of deposits on the lower surfaces of the valve heads can also cause a loss of compression pressure.
11. If the measurement results are below the allowable value, you should try to determine the cause of the pressure loss. The most elementary of the checks is to pour about one teaspoon of engine oil through the spark plug hole into the corresponding cylinder, followed by repeating the measurement of compression pressure.
12. If immediately after adding oil to the cylinder, the compression pressure is temporarily restored, the degree of wear of the pistons, cylinder walls and piston rings should be assessed. Otherwise, we can talk about a violation of the tightness of the closing of the valves (for example, as a result of burnout) or damaged cylinder head gasket (or the head itself).
13. Equally low pressure in two adjacent cylinders with a high degree of probability indicates damage to the cylinder head gasket jumper located between them. The presence of coolant in the engine oil will confirm this assumption.
14. If the pressure in one of the cylinders is approximately 20% lower than in the others, and the stability of the engine idle speed is slightly disturbed, the wear of the corresponding camshaft cam lobe may be the cause of this phenomenon.
15. Excessively high compression pressure indicates strong carbon formation in the combustion chambers. In this case, the head should be removed and subjected to decarbonization.
16. Finally, screw in the spark plugs, reinstall the fuel pump relay and start the ignition system.