Compression in cylinders — check (Audi A6 C5)

Compression testing allows you to draw conclusions about the engine's condition. Based on the results of the test, you can judge whether the engine has exhausted its resource and is subject to replacement or major repairs. During the test, it is important to find out whether the compression in all cylinders is the same or whether it is different. To check the pressure in the cylinders, you need a compression tester, which is offered by specialized stores.

Attention! To check the compression on diesel engines, a compression tester with a large measurement range, up to approximately 40 bar, is required.

The pressure data obtained during measurement on each cylinder of a diesel engine should not differ by more than 5 bar. If the pressure in one or more cylinders differs from the pressure in other cylinders by more than 5 bar, this indicates a defect in the valves, wear of the piston rings or working surfaces of the cylinders, as well as the cylinder head gasket.

When performing a compression test, the engine oil temperature should be at least +30°C. At this oil temperature, the oil filter is warm enough to the touch. Warm up the engine if necessary.

1. Remove the engine protective cover by removing the plugs and unscrewing the nuts (see arrows in the illustration).

7.1 Remove the engine protective cover by removing the plugs and unscrewing the nuts (see arrows)

2. Disconnect the power wire from the fuel shut-off valve from the injection pump so that fuel is not injected during the compression test.

3. Disconnect the glow plug power connectors and carefully unscrew the glow plugs.

4. Attach the flexible hose of the compression tester to the glow plug socket (see illustration).

7.4. Secure the flexible hose of the compression tester to the glow plug socket

Attention! The compression value specified in the specifications is valid when checking the compression pressure in the cylinders using the VAG 1763 compression tester. To connect the compression tester to the glow plug sockets, use the VAG 1763/5 adapter (see illustration 7.4). When performing a compression test with other devices, you can only find out the difference between the compression in individual cylinders.

5. Let the engine turn over approximately 8 revolutions until the pressure registered by the compression gauge stops increasing. Read the compression gauge readings.

6. Install the removed components in the reverse order of removal.