Compression check (Audi A6 C4)

Compression testing allows you to draw conclusions about the engine's condition. Namely, when checking, you can determine whether the valves and pistons are in order (piston rings), or they are worn out. In addition, the test results show whether the engine needs to be replaced or a complete overhaul. A compression tester is required for testing, which is available in specialized stores at an affordable price for gasoline engines.

The maximum permissible pressure difference in individual cylinders can be 3.0 bar (for diesel engines 5.0 bar). If one or more cylinders have a pressure difference of more than 3.0 bar compared to others, this indicates defective valves, worn piston rings or cylinder running surfaces. If the wear limit is reached, the engine must be repaired or replaced.

Engine	Compression pressure, bar (new)	Compression pressure, bar (wear limit)
Petrol 6-cylinder	11–16	9

The compression test must be performed on a warm engine. The engine temperature must be at least 30°C.

Execution order

1. Turn off the ignition.

2. Pull out the ignition coil voltage output stage plug. The voltage output stage is located next to the ignition coil. For a 6-cylinder engine, you need to pull out 2 plugs.

3. Remove fuse N17 (for fuel pump) from the fuse box.

4. Remove all electrical connectors from the valve injectors. On engines with the Mono-Motronic system there is only one valve injector.

5. Pull out all spark plug plugs. There is a special rod for this, for example HAZET 1849.

6. The plugs must then be placed into the steel sockets, if available.



7. After this, blow out the spark plug recesses in the cylinder head with compressed air and unscrew all the spark plugs with a suitable wrench.

8. Turn the engine over a couple of times with the starter to flush out any carbon deposits and soot.

Warning: Shift the gearbox into neutral and apply the handbrake.

9. Press the compression gauge against the spark plug hole or screw it in according to the service manual. The assistant should fully depress the gas pedal and hold it with his foot during the entire test.

10. Turn the engine over approximately eight revolutions until the readings on the instrument scale stop changing.

11. Check all cylinders in sequence and compare the obtained values with the recommended ones.

12. After this, screw in the spark plugs and insert the spark plug wires.

13. Insert the voltage output stage plug.

14. Insert the valve injector plug.

15. Insert fuse N17 into the fuse box.