Caution: A diesel engine requires a compression tester with a larger measurement range, up to approximately 40 bar. The difference in compression in individual cylinders should not exceed 1.0 bar (for a diesel engine: 3.0 bar). If the compression of one or more cylinders differs from the compression in others by more than 1.0 bar (diesel engine 3.0 bar), a valve defect, worn piston rings or cylinder surface may be suspected. When the wear limit is reached, the engine must be overhauled or replaced.
Compression pressure in bars
Warm up the engine to operating temperature. To do this, drive the car until the coolant reaches normal operating temperature. The readings should be 80° + 90°C.
Turn off the ignition.
Gasoline engine
Remove the spark plug wire tips from all the spark plugs. There are special pliers for this, for example, HA-ZET 1849. However, they can only be used for metal sleeves, if any.
Disconnect the ignition wires from the ignition coil.
Engine with fuel injection device: Disconnect power from the fuel pump, remove the relay connector. For the location of the relay, see section 8.8.
Blow out the spark plug recesses with compressed air and remove all the spark plugs.
Turn the engine over several times with the starter to throw out residues and carbon deposits.
Warning: Set the gearbox to neutral, apply the handbrake. When cranking the engine, do not lean over the spark plug holes, there is a risk of injury from ejected coolant or oil (if the cylinder walls are defective). For safety, cover the spark plug holes with a rag.
According to the operating instructions, insert or screw the compression gauge into the spark plug hole.
The assistant presses the gas pedal. The gas pedal must be pressed during the entire test.
Operate the starter to crank the engine approximately 8 revolutions until the compression gauge reading reaches its maximum value.
Check all cylinders in sequence and compare with the specified value.
If the compression is below the wear limit, pour some oil into the spark plug holes and repeat the compression test. If the compression increases after adding oil, the piston rings and/or cylinder walls may be worn. If the compression does not increase, the valve or cylinder head gasket is usually defective.
Screw in the spark plugs and connect the ignition wires, see item 5/32.1.
Place the ignition wire onto the ignition coil.
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Install the fuel pump relay connector.
Diesel engine
Remove the upper part of the intake manifold, see p. 1.10.
Remove the electrical wire from the high-pressure fuel pump (HPFP) switch.
Clean the injection tubes with a cleaner and remove them as a set, without damaging their curvature, see item 9.10.
Remove the injectors, see item 9.10.
Remove the holder gasket and the injector seal from the injection hole.
Crank the engine with the starter to push out the residue and carbon deposits.
Warning: Set the gearbox to neutral, apply the handbrake. When cranking the engine, do not lean over the spark plug holes - there is a risk of injury from ejected coolant or oil (if the cylinder walls are defective). For safety, cover the holes with a rag.
Screw the nozzle into the injection nozzle hole, then screw the compression gauge onto the nozzle.
The assistant must press the gas pedal all the way down and keep his foot on the pedal throughout the entire test.
Turn the engine at starter speed (~250 rpm) until the instrument readings stop increasing.
Check the compression in all cylinders sequentially and compare with the specified value.
If the compression is below the wear limit, pour some oil into the injector holes and repeat the compression test. If the compression increases after adding oil, the piston rings and/or cylinder walls may be worn. If the compression does not increase, the valve or cylinder head gasket is usually defective.
Install the injectors, see item 9.10.
Install injection tubes.
Install the upper part of the intake manifold, see p. 1.10.
Place the electrical wire on the fuel injection pump switch.