Caution: For diesel engines, a compression tester with a measurement limit of up to approximately 40 atm is required.
The engine must be warmed up to operating temperature, the battery must be fully charged. You will also need the help of an assistant.
The maximum allowable pressure difference in the individual cylinders can be 3.0 atm. (for diesel engines 5.0 atm.).
Compression pressure in a serviceable engine rises very quickly. A low reading after the first cycle, increasing with successive cycles, indicates worn piston rings. A low value after the first cycle, not increasing after the next, signals that either the valves are leaking or the head gasket is blown (Could also be a cracked head). The presence of soot on the valve plates can lead to a decrease in compression.
Please note that due to different starter rotation speeds on different models, the results obtained as a result of measurements may differ. The results obtained when measuring compression should be approximately the same for all cylinders.
If the pressure in any cylinder is at or below the minimum allowable pressure, follow these steps to determine the cause. Pour a teaspoon of engine oil into the cylinder through the spark plug hole and repeat the compression measurement.
If the addition of oil temporarily improves compression, the cause of the decrease is most likely piston, ring, or cylinder wear. If there is no increase in compression, then it can be assumed that the cause is valve leaks or a broken head gasket.
Low compression in two adjacent cylinders is almost certainly the result of a blown head gasket. The presence of coolant in the combustion chambers or in the crankcase will confirm this assumption.
If the compression in one of the cylinders is about 20% lower than in the others, besides, the idle speed is unstable, then the cause may be excessive wear of the camshaft cam.
After completing the check, reinstall the spark plugs (contact the head Ongoing care and maintenance, put on them tips of high-voltage wires, connect the connector to the ignition coil. Reinstall the plastic engine cover and fuel pump fuse.
Compression pressure values for various engines are given in Specifications.
Gas engine
1. Turn off the ignition.
2. Engine 1.6 l: Disconnect the ignition coil output stage connector. The output stage is in the same housing as the ignition coils on the engine.
3. Remove the No. 28 fuel pump fuse.
4. Engine 1.8 l: Disconnect the connectors of the ignition coils and injectors.
5. Engines 2.0, 2.4 and 3.0 l: Remove ignition coils. Disconnect the injector connector.
6. Remove all spark plugs, refer to Section Checking and replacing spark plugs. Checking the condition of high-voltage wires.
Caution: When cranking the engine, do not lean over the engine. There is a risk of injury due to the ejection of soot particles.
7. Turn the engine over with the starter to remove carbon and soot.
Caution: Place the transmission in neutral and apply the parking brake.
8. Screw the compression tester in accordance with the manufacturer's instructions into the spark plug hole.
9. Ask an assistant to press the gas pedal and hold it with your foot during the check.
10. Turn the engine about 8 revolutions so that there are no more pressure surges on the compression gauge.
11. Consistently check all cylinders and compare the obtained pressure values with the given ones.
12. Replace the spark plugs and tighten them with torque 30nm, refer to Section Checking and replacing spark plugs. Checking the condition of high-voltage wires.
13. Reconnect all disconnected connectors, if necessary, replace the fuse.
Caution: If the connectors are disconnected, fault data is stored in the engine control unit. It is recommended that the recorded data be deleted at an AUDI workshop as soon as possible.
Diesel engines
1. Engine 1.9 l: Disconnect the central motor connector. To do this, turn the knurled screw to the left. Disconnect the spark plug connector.
2. Engine 2.5 l: Disconnect the injection pump connector.
3. Remove all glow plugs, refer to Section Removal and installation of glow plugs.
4. Screw in the compression tester with flexible connection instead of the glow plugs.
Caution: Specified in Specifications The compression values correspond to those measured with a VAG compression tester Deviations may occur if other measuring instruments are used. In this case, it will only be possible to measure the pressure spread in individual cylinders.
5. Turn the engine about 8 revolutions until there are no more pressure surges on the compression gauge.
6. Replace the glow plugs and torque them 15Nm. Connect the wire.
7. Connect and secure all connectors.
Caution: When the connectors are disconnected, fault data is recorded in the engine control unit. It is recommended to read and delete the recorded data as soon as possible.
Leak test
During this test, the rate of exit from the cylinders of the compressed air pumped into them and the leaks directly are determined. This test is an alternative to the compression test. Moreover, from many points of view, it is much more effective, since visually identifying the source of a leak is easier than comprehending the results of a compression measurement.
The equipment needed to test for leaks is not publicly available, so this test will have to be entrusted to the service center specialists.
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