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3 Design and Function
3.3 Application: Compression test in diesel engines
Follow the instructions provided by the vehicle
manufacturer during any work you do!
3.3.1 Before starting the operation
• Injection system must be disconnected from the fuel supply! No fuel may be injected.
The engine can start and this can cause injuries!
• The engine of the vehicle must be in an operating temperature state for all works.
Risk of burns when the engine is at operating state temperature, do not touch any hot parts.
• Allow engine to warm up. Apply the vehicle handbrake.
• The engine is switched off!
• Disassemble all of the cabling of the injectors and the injection nozzles. If necessary,
remove the the injectors or glow plugs. Please follow the instructions of the manufacturer.
Caution: With live parts there is a danger of electric shock!
• Follow the installation / removal sequence when removing the injectors or glow plugs.
3.3.2 Application: Compression test in diesel engines
• Remove a suitable adapter if necessary and screw the manometer with hose finger-tight
into the injector or glow plug thread.
• Start the engine and at the same time give it full power until the pointer of the manometer
no longer rises and no further compression is built up.
• Make a note of the displayed values and perform the test on the remaining cylinders.
• To do this, proceed as previously described.
3.3.3 Test results
• Observe the vehicle manufacturer‘s instructions.
• With intact cylinders, the maximum compression should be reached immediately
after starting.
• The piston must be checked for damage when there is no compression on the cylinder.
A combustion temperature that is too high and uncontrolled combustion can damage
the piston.
• If the compression is lower for two opposing cylinders than for the rest of the cylinders, the
cause may be the result of a defective cylinder head gasket in the transition area. For
this reason, the cylinder must also be checked for oil and water residue. This also indicates
a defective cylinder head gasket.
• If the compression of a cylinder is lower than that specified by the manufacturer, add a
little oil into the combustion chamber and check the compression again. If a significantly
higher compression is achieved, the cause may be worn piston rings. If the compression
remains unchanged, a valve may be damaged or there may be a defect in the camshaft.
• If the measured compression for all cylinders is below the manufacturer‘s specifications, this
may be a result of age-related wear of the engine. The engine can be disassembled and
surveyed for the exact diagnosis.
• After completing the compression test, again assemble all of the disassembled components
in the prescribed sequence. Follow the instructions provided by the vehicle manufacturer!
Summary of Contents for V4461
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