Attention: For a diesel engine, a compression gauge with increased measuring limits is required.
The compression pressure may vary depending on the compression gauge used and the starter RPM. The compression pressure is 11-13 bar for petrol engines and 20-25 bar for diesel engines. More informative is the difference in compression between the individual cylinders.
The pressure difference between the individual cylinders must not exceed 3.0 bar (diesel - 5.0 bar). If one or more cylinders have a pressure difference of more than 3.0 bar compared to the others (diesel 5.0 bar), this indicates faulty valves, worn piston rings or cylinder bores. If the wear limit is reached, the engine must be repaired or completely replaced.
To check the compression, the temperature of the engine oil must be at least 30°C, i.e. the engine must be warm.
Valve clearance must be correct - adjust if necessary.
Gasoline engines
Switch off the ignition.
Pull out the fuel pump relay.
Start the engine. It will start and stop when the fuel pump does not supply fuel and there is no fuel pressure in the system. This measure will prevent unburned fuel from entering the engine and exhaust system.
Disconnect wires (1) And (2), if any, from the ignition coil.
Remove spark plugs.
Turn the engine over a little with the starter to remove deposits and soot from it.
Attention: The transmission must be in neutral and the parking brake must be applied.
In accordance with the operating instructions, press the compression tester into the spark plug hole or screw it into the hole.
Have an assistant fully depress the pedal «gas» and hold it in this position during all measurements.
Crank the engine a few revolutions until the compression gauge shows the maximum value.
Check all other cylinders in this way and record the values obtained.
Finally, install the spark plugs.
Install the fuel pump relay.
Attention: When starting the engine with the fuel pump relay/ignition coil plugs removed, the engine management system self-diagnostic unit stores fault codes. Fault codes must be erased in a workshop. If the trouble codes are not erased, then this will not lead to a deterioration in engine performance.
Diesel engine
Turn the ignition key to position «0».
Disconnect the electrical wire from the injection pump fuel cutoff valve.
Disconnect the wires for the glow plugs and arrange them separately.
Disconnect the wires from the glow plugs and unscrew the glow plugs.
Screw in the compression gauge instead of the glow plug and turn on the starter until the compression gauge stops rising. Check all cylinders in this way.
Put the ignition key in position «ABOUT».
Install glow plugs.
Connect the wires to the fuel shut-off valve and to the glow plugs.