Compression test

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1. In the event of deterioration in engine performance or in the event of ignition failures, the cause of which cannot be attributed to the ignition system or fuel system, a compression test is a means of diagnosing the condition of the engine. Carrying out this check regularly helps prevent serious malfunctions.

2. The engine must be warmed up to normal operating temperature, the battery must be fully charged. All spark plugs must be removed (see chapter 1). In addition, you will need an assistant for this work.

3. Turn off the ignition system. To do this, disconnect the ignition coil connector. Also pull out fuse no. 14 to disconnect the fuel pump.

4. Install the compression tester in the spark plug hole of the 1st cylinder. A compression gauge that is screwed into the threaded hole of the spark plug is more preferable.

5. Ask the assistant to fully depress the accelerator pedal and turn on the starter. After one or two revolutions, the pressure in the cylinder should increase to a maximum, after which its value will stabilize. Record the maximum meter reading.

6. Repeat the test in all other cylinders, recording the pressure values in each of them.

7. At the time of writing this manual, there was no exact information about the pressure in the cylinders, but it is known that it should not exceed 12 bar. Pressure readings in different cylinders should be close in magnitude. The maximum difference between any two cylinders must not exceed 10%. Keep in mind that a healthy engine should build pressure quickly. Low pressure during the first stroke, followed by a gradual increase in subsequent strokes, indicates wear on the piston tracks. If the pressure is low after the first stroke and does not increase on subsequent strokes, this indicates leaks through the valves or through the head gasket (the reason for this may also be damage to the block head itself). The presence of deposits on the undersides of the valve heads can also cause low pressure.


8. If the pressure in one of the cylinders is reduced, perform an additional check to identify the cause of this. Pour a little clean oil into such a cylinder through the hole of the candle (about a teaspoon) and recheck.

9. If a temporary increase in pressure occurs when oil is added, this indicates excessive cylinder or piston wear. If the pressure does not increase, then the cause may be leaks through burnt valves or through the head gasket.

10. Low pressure in two adjacent cylinders almost certainly indicates leakage through the gasket in the area between them. The presence of coolant in engine oil is a confirmation of this assumption.

11. A decrease in pressure in one of the cylinders by about 20% relative to other cylinders, as well as not quite smooth engine idling, can be caused by wear on the camshaft cam.

12. Too high a pressure value may be due to a thick layer of carbon deposits on the walls of the combustion chamber. In this case, it is necessary to remove the block head and remove carbon deposits.

13. At the end of the test, install the candles. Repair the connection between the ignition system and the fuel pump.







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