Make sure that the starter provides a normal engine speed of at least 250 min⁻¹.
The compression test must be performed on a cold engine.
Disconnect the terminals from the battery.
Disconnect the computer that controls the engine.
Disconnect power from the glow plugs.
Insulate the glow plug wire.
Remove the plastic windshield crossbar.
Remove the decorative engine cover.
Remove the upper integrated air intake system.
Remove the exhaust gas recirculation system connection pipe.
Remove the glow plug supply bus.
Remove the glow plugs.
Install a dummy glow plug and a FACOM 910.A6 compression tester adapter into cylinder 1 instead of the glow plug.
Tighten the spark plug to a torque of 10 Nm.
Connect the adapter to the 0188-U compression tester.
Connect the terminals to the battery.
Compression is measured by turning the crankshaft with the starter. After two revolutions, the compression should reach its maximum value (20–22 bar) and remain unchanged. On a properly functioning diesel engine, the pressure should build up quickly. Low pressure after the first piston stroke and a slow increase during subsequent compression strokes indicates wear of the piston rings. If the pressure is low after the first stroke of the piston and does not increase during subsequent compression strokes, then the cause is a leak in the valves or a leak in the cylinder head gasket.
The permissible difference in compression between cylinders should not exceed 5 bar. Keep in mind that elevated pressure gauge readings indicate heavy carbon deposits in the combustion chambers and the need for disassembly and cleaning.
The cause of compression loss in a diesel engine is more difficult to determine than in a gasoline engine (an increase in compression after introducing oil into the cylinder is not decisive, since the oil can settle on the walls of the swirl chamber or in the recesses of the piston bottom and not reach the piston ring area).
If the compression is below normal, the test should be supplemented with leak tests by measuring the leak rate of air pumped into the cylinder under high pressure. This procedure is performed exclusively in a car service center.