Table of contents: Compression check ↓ Checking for leaks ↓
Compression check
Note: Use a special compression tester designed for diesel engines.
1. If the engine is not producing full power or is running rough, and the problem is not related to the fuel system, a compression test will help you identify the problem. If you do this regularly, you can identify the problem before it causes serious damage.
2. Use a special compression tester designed for diesel engines, as these engines develop much higher pressure. The compression tester is equipped with adapters that are screwed into the hole for the glow plug or injector.
3. If the compression tester is not supplied with manufacturer's instructions, perform the following preparation:
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 injectors and shielding washers (the latter may otherwise fly out under pressure).
c) The fuel shut-off valve must be turned off to prevent accidental engine starting or fuel leakage.
4. There is no need to keep the accelerator pedal depressed during the test because it is not connected to the air supply to the engine.
5. Manufacturers provide a minimum compression value - see Specifications. Consult your Audi dealer for advice if there is any doubt about the test results.
6. It is more difficult to determine the cause of low compression on a diesel engine than on a petrol engine. Pouring oil into the cylinders is not very indicative, since the oil may linger in the recess on the piston head and not reach the rings. However, the following information will help you identify the possible cause of the malfunction.
7. There should be approximately equal pressure in all cylinders; a difference of more than 5 bar between any two cylinders indicates a malfunction. Note that compression in a healthy engine increases quickly; low compression on the first revolution and its subsequent gradual increase indicates wear of the piston rings. If the compression remains low, the valves or cylinder head gasket are burnt out, or the head is cracked.
8. Low compression in two adjacent cylinders is almost certainly caused by a blown head gasket between them.
Checking for leaks
9. A leak test determines what percentage of the air supplied to the cylinder is lost. This test is an alternative to a compression test and is superior in many ways. It allows you to determine where the loss of pressure occurs (piston rings, valves or cylinder head gasket).
10. The equipment required to test for leaks is unlikely to be available to a car enthusiast. Therefore, you should contact a properly equipped car repair shop to conduct the test.
(A link to the original source is available on the website Audimanual.ru)