Compression, Checking: Procedure
- Engine oil temperature at least 30 °C.
- Battery voltage minimum 12.5 V.
Vehicle with high-voltage system:
- Audi A8: removing the throttle valve control module. Refer to Throttle Valve Control Module -GX3-, REMOVING AND INSTALLING .
- Audi Q7/Q8: removing the air duct pipe from the throttle valve control module. For corresponding procedures refer to Throttle Valve Control Module -GX3-, REMOVING AND INSTALLING . Release and disconnect the connector from the throttle valve control module.
-- Audi Q7/Q8: open the throttle valve by hand and lock while opened using the Trim Removal Wedge :3409 or a wooden wedge -arrow-. Appropriately secure the Trim Removal Wedge :3409 or the wooden wedge using a string.
Risk of destroying the engine due to accidentally sucked in foreign objects while the throttle valve control module is open or removed.
- Make sure that no foreign objects are located in the work area and that the trim removal or wooden wedge is secured.
-- Connect the Vehicle diagnostic tester and switch on the ignition.
-- Select the Diagnostic mode and start the diagnosis.
-- Select the Test plan tab.
-- Select the Select individual test button and select the following tree structure consecutively:
- Diagnostic-capable systems
- 0001- Engine Management Engine/Motor Control Module -J623-
- 0001 - Engine electronics functions
- 01-Activate/deactivate the service mode
Continuation for all:
-- Remove the fuse for the Fuel Pump Control Module -J538-. Refer to the appropriate Wiring Diagram.
-- Remove the ignition coils. Refer to IGNITION COILS, REMOVING AND INSTALLING .
-- Remove the spark plugs using the Spark Plug Socket Adapter 3/8" :VAS 6919 .
With Compression Tester Kit - Adapter :V.A.G 1763/12 :
-- Install the Compression Tester Kit :V.A.G 1763 as shown in the corresponding spark plug connectors.
With Compression Tester Kit - Adapter :V.A.G 1763/12A :
-- Install the Compression Tester Kit :V.A.G 1763 as shown in the corresponding spark plug connectors.
Continuation:
-- Check the compression using the Compression Tester Kit :V.A.G 1763 . Refer to the Operating Manual.
- The help of a second technician is necessary for the following step.
-- Have a second technician hold for so long, until the tester shows there is no longer an increase in pressure.
-- Repeat the procedure on each cylinder.
| Compression pressure | bar pressure | |
|---|---|---|
| 2.9L engine | 3.0L engine | |
| New | 12.0 to 17.0 | 14.0 to 18.5 |
| Wear limit | 10.0 | 12.0 |
| Maximum difference between cylinders | 3.0 | 3.0 |
TIP
If the test with the Compression Tester Kit :V.A.G 1763 does not lead to a clear result there are two additional tests.
- In addition to the compression test a pressure test can be performed with the Pressure-Loss Tester :VAS 522 001 . The procedure for this is described in the operating instructions for the Pressure-Loss Tester :VAS 522 001 .
- As an additional test the CO2 content in the coolant expansion tank can be measured. A raised CO2 content in the cooling system indicates a leak between the combustion chamber and the cooling system. The CO2 content can be determined using the CO2 Coolant Tester :VAS 531 009 . The procedure for this is described in the operating instructions of the CO2 Coolant Tester :VAS 531 009 .
Assemble in the reverse order of removal. Note the following:
-- Install the spark plugs. Refer to OVERVIEW - IGNITION SYSTEM .
-- Install the ignition coils. Refer to IGNITION COILS, REMOVING AND INSTALLING .
-- Install the fuse for the Fuel Pump Control Module -J538-. Refer to the appropriate Wiring Diagram.
-- Delete DTC entries which were generated during testing using the Vehicle diagnostic tester .