Compression in the cylinders — check (Audi A6 C5 Allroad)

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

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

The measured pressure data on each cylinder of a diesel engine must 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, then 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 temperature of the engine oil must be at least +30°C. At this oil temperature, the oil filter is quite warm to the touch. Warm up the engine if necessary.

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




2. Disconnect the power wire from the fuel cutoff valve from the injection pump so that no fuel is injected when performing a compression test.

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

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

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 instruments, you can only find out the difference between the compression in individual cylinders.

5. Allow the engine to complete about 8 revolutions until the increase in pressure recorded by the compression gauge stops. Read the pressure gauge readings.

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

Table of compression values

Engine	Compression, bar nominal value	limit value
AFB, AKN	27-30	20
AKE, AYM, BAU, BCZ, BFC	26-29	19
BDG, BDH	24-27	17