The maximum permissible pressure difference in the individual cylinders can be 3.0 bar (for diesel engines 5.0 bar). If one or more cylinders have a pressure difference greater than 3.0 bar compared to the others, this is an indication of defective valves, worn piston rings or cylinder sliding surfaces. If the wear limit is reached, the engine must be repaired or replaced.
Engine | Compression pressure, bar (new) | Compression pressure, bar (depreciation limit) |
Petrol 6-cylinder | 11–16 | 9 |
The compression test should be done with the engine warm. The engine temperature must be at least 30°C.
Order of execution
1. Switch off the ignition.
2. Pull out the ignition coil voltage output stage plug. The voltage output stage is located next to the ignition coil. With a 6-cylinder engine, 2 plugs must be pulled out.
3. Remove fuse N17 (for fuel pump) from the fuse box.
4. Pull out all electrical plugs of valve injectors. On engines with the Mono-Motronic system, only one valve injector is available.
5. Pull out all spark plug plugs. There is a special rod for this, for example HAZET 1849.
6. Then the plugs must be placed in steel sockets, if any.
7. After that, blow out the spark plug recesses in the cylinder head with compressed air and remove all the spark plugs with a suitable wrench.
8. Crank the engine a couple of times with the starter to expel carbon deposits and soot.
Warning: Shift the transmission to neutral and apply the handbrake.
9. Compressometer in accordance with the service manual, press against the spark plug hole or screw in. The assistant must completely drown the gas pedal and hold it with his foot throughout the test.
10. Turn the engine about eight revolutions until the change in readings on the instrument scale stops.
11. Check all cylinders in series and compare the obtained values with the recommended ones.
12. Then screw in the spark plugs and insert the ignition wires.
13. Plug in the plug of the voltage output stage.
14. Plug in the valve injector plug.
15. Insert the N17 fuse into the fuse box.
Visitor comments