Using a Compression Pressure Tester to Check Compression in Diesel Engine Cylinders
Checking the condition of the engine can be done by measuring the compression pressure in the engine cylinders. If this check is carried out regularly, it is possible to know in advance the beginning of engine wear, without waiting for the moment when engine wear manifests itself in low engine efficiency.
Warm up the engine to operating temperature. In this case, the battery must be fully charged.
Remove all spark plugs.
Engines 1.6-I
Disconnect the electrical connector from the ignition coil.
Five-cylinder engines
Remove the air pipe located between the air filter and the air intake, for which loosen the clamps and disconnect the electrical connector from the air flow meter. Remove the air pipe together with the crankcase ventilation valve.
Five- and six-cylinder engines
Disconnect the electrical connector from the ignition control unit. The ignition control unit is located in the electrical circuit between the control unit and the ignition coil.
Six-cylinder engines
Disconnect all electrical connectors from the fuel injectors or remove the No. 28 fuse located in the fuel pump power circuit.
Engage neutral gear and apply the handbrake.
Install a compression gauge or compression pressure tester in the spark plug hole of the first cylinder.
The assistant should press the accelerator pedal to the stop and turn the engine with the starter. After cranking the crankshaft one or two revolutions, the compression pressure should increase to maximum and then stabilize. Record your maximum score.
Check the compression in the other cylinders in the same way.
The compression pressure in all cylinders of petrol engines should not differ by more than 3.0 bar, and in a diesel engine - 5.0 bar. Note that the amount of compression should increase rapidly on a healthy engine. Low compression pressure on the first revolution of the crankshaft, followed by a gradual increase in pressure on subsequent revolutions of the crankshaft, indicates worn piston rings.
A low pressure value at the first revolution of the crankshaft, which increases slightly thereafter, indicates a valve leak, a blown cylinder head gasket, or a crack in the cylinder head. Worn valve stem ends can also result in low compression pressure.
If the pressure in one cylinder is low, then carry out the following tests. Pour some engine oil through the spark plug hole into the cylinder and check the compression pressure.
If pouring oil into the cylinder increases the compression pressure, this indicates that the cylinder or piston rings are worn.
Low pressure in two adjacent cylinders indicates a burnt gasket between the cylinders.
If the pressure in one cylinder is less than 20% than in the others, and the engine runs erratically at idle, this indicates a worn camshaft cam.
If the compression pressure is too high, this indicates that the combustion chamber is covered with a thick layer of soot.
After this check, screw in the spark plugs.
Connect the electrical connector to the ignition coil control unit. On a six-cylinder engine, connect the connectors to the fuel injectors or install a fuse in the fuel pump circuit.
Five-cylinder engines
Reinstall the air hose and secure it with clamps. Connect the electrical connector to the air flow meter.
Warning: After disconnecting the electrical connectors for the ignition and fuel injection system, a fault message is recorded in the electronic engine control unit. It is recommended to erase the fault information stored in the memory at a specialist workshop as soon as possible "Volkswagen".
Diesel engine
Disconnect the electrical connector from the engine stop valve.
Disconnect the electrical connector from the flow meter on the fuel pump.
Unscrew all glow plugs.
Instead of glow plugs, screw in a compression pressure tester with a flexible adapter hose, see fig. Using a compression pressure tester to check the compression in the cylinders of a diesel engine.
Turn the crankshaft of the engine with a starter until the pressure recorded by the measuring device stabilizes. Record your result.
Check the compression in the other cylinders in the same way.
Screw in the glow plugs, tightening them to a torque of 15 Nm and connect the voltage supply rail to the glow plugs.
Connect all previously removed electrical connectors.
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