Compression test
Note: Use a special compression tester designed for diesel engines.
1. If the engine does not develop full power or runs unevenly, and the malfunction is not related to the fuel system, a compression test will help you identify the malfunction. If you check regularly, you can identify the problem before it leads to serious damage.
2. Use a special compression tester designed for diesel engines, because. these engines develop much higher pressures. The compression tester is equipped with adapters that are screwed into the hole for the glow plug or nozzle.
3. If the compression gauge is not supplied with the manufacturer's instructions, perform the following preparations:
a) Make sure the battery is fully charged and the air filter is not clogged, and warm up the engine to normal operating temperature.
b) Before starting the test, remove all nozzles, as well as shielding washers (the latter may otherwise fly out under pressure).
c) The fuel cut-off valve must be disabled to prevent accidental starting of the engine or fuel leakage.
4. It is not necessary to keep the accelerator pedal depressed during the test because it is not connected to the air supply to the engine.
5. Manufacturers give a minimum compression value - see Specifications. Seek advice from an Audi dealer if there is any doubt about the test results.
6. The cause of low compression on a diesel engine is more difficult to establish than on a gasoline one. Pouring oil into the cylinders is not very revealing, since the oil can linger in the recess on the piston head and not pass to the rings. However, the following information will help you identify the possible cause of the problem.
7. All cylinders should have approximately equal pressure; a difference of more than 5 bar between any two cylinders indicates a malfunction. Note that compression in a healthy engine rises rapidly; low compression on the first revolution and its subsequent gradual increase indicates worn piston rings. If compression remains low, the valves or cylinder head gasket are burnt, or the head is cracked.
8. Low compression in two adjacent cylinders is almost certainly caused by a burnt head gasket between them.
Leak test
9. The leak test determines what percentage of the air supplied to the cylinder is lost. This test is an alternative to the compression test and is superior to the latter in many ways. The test allows you to determine where the pressure loss occurs (piston rings, valves or cylinder head gasket).
10. The equipment needed to test the tightness is hardly available to a motorist. Therefore, to carry out the test, you should contact a suitably equipped workshop.
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