Compression Check: Testing and Inspection

WM 101902 Checking compression of cylinders





Preliminary work

Preliminary work

1. Open the bonnet.
2. Open lid of central electrics box. To do this, loosen the four fastening screws.





Central electrics box

Warning:
Risk of electric shocks from high-voltage ignition system and danger of damage to ignition rod modules!
Connected ignition rod modules can be damaged.

- Always remove the ignition rod module fuse.

- Always disconnect ignition rod module electrical connections.

Caution:
Risk of damage to components that affect the exhaust system!
Unburnt injected fuel enters the exhaust system.

- Prevent the fuel from injecting by removing the fuse.

3. Remove the fuses -7- for the ignition rod modules -8- and injection system.





Fuses for ignition rod modules and fuel injectors

4. Remove spark plugs.





Spark plugs

Tools and materials

Tools and materials





Tools for testing pressure loss





Information

Evaluating test results and prerequisites for testing

Information:
A test document is created when a compression test is performed.
In order to prevent misuse, vehicle ID, date and current mileage must be entered.





Test sheet





The throttle must remain open during the test.
The vehicle voltage must remain more or less constant during the test (connect a charger).
The vehicle voltage must not drop below 12 V.
The fuses for the injection system and the ignition system must be removed during the test.
The engine must be at operating temperature.

Testing engine compression

Testing engine compression

Information:
The compression test can only issue information regarding whether the cylinder being tested is OK or not OK. Further localization of the cause of loss is achieved by a pressure loss test or a compression chamber endoscopy.

1. Press pressure tester onto the relevant cylinder.





Pressure tester

Information:
Once the starter is activated, it switches on the engine for approx. seven seconds.
This process should not be interrupted.
The vehicle voltage must not drop below 12 V during the test.
The throttle must always remain in the same position throughout the test. A mechanical pressing-on tool is not permitted.
The accelerator pedal must be fully depressed during the test.

2. Have the starter actuated by a second person. Testing of this cylinder is complete when the needle of the test device ceases to rise. Keep the accelerator pedal fully depressed.
3. Deflate the pressure on the tester.
4. Move the scale on to another cylinder. To do this, pull the pin once under the handle on the back.





Moving the test device on by one cylinder

5. Then check the next cylinder according to number sequence (not according to firing order).

Subsequent work

Subsequent work

1. Fit spark plugs.





Spark plugs

2. Fit the ignition rod module fuses and the injection system.





Fuses for ignition rod modules and injection valves

3. Fit lid of central electrics box.





Central electrics box