Checking Compression of Cylinders

Performing compression pressure check on DFI engines





Preliminary work

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





Central electrical 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!
^ Unburned injected fuel enters the exhaust system.

-> Prevent the fuel from injecting by removing the fuse.

3. Pull out the fuses for the ignition rod modules and the injection system. For latest assignment, see wiring diagram.
4. Remove spark plugs.

Tools and materials

Tools





Tools for testing pressure loss

A - Spark plug wrench 3122 B
B - Moto-Meter Compression Recorder WE 1065
C - Flexible extension Moto-Meter Compression Recorder WE 1065
D - Extension with spark plug thread M12 x 1.25 Moto-Meter Compression Recorder WE 1065

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

A - Vehicle ID -> This is used to assign the test diagram to the vehicle that is being tested. The engine number or the chassis number can be entered here instead of the vehicle ID.
B - Date
C - Mileage
I - Compression pressure reached in the cylinder that is being tested in bar (1 bar = 14.5 psi). There are different charts. The charts for petrol engines are used.
II - Difference in pressure between the individual cylinders -> maximum permissible pressure difference between 2 cylinders is 3 bar.

^ The throttle valve must remain open during the test.
^ The engine should have a crank drive that has been run in. Mileage at least 2000 km.
^ 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.
^ Electrical loads switched off.
^ Air conditioning switched off.

Test values

1) The compression values are heavily dependent on: Amount of deposits in combustion chamber, state of the combustion chamber seal (valves, piston rings, etc.), starter speed, engine temperature, engine mileage etc.

^ New, bar overpressure = 11.0 to 13.0
^ Wear limit, bar overpressure = 8.0
^ Maximum difference between the cylinders, bar overpressure (within one measurement) = 3.0

Testing engine compression

Information:
^ This process should not be interrupted.
^ The vehicle voltage must not drop below 12 V during the test.
^ The throttle valve 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.
^ The throttle valve must remain open during the test
^ The vehicle voltage must remain more or less constant during the test (connect a charger).
^ The fuses for the injection system and the ignition system must be removed during the test
^ The engine must be at operating temperature.
^ Electrical loads switched off
^ Air conditioning switched off

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. Connect pressure tester to the corresponding cylinder via the extensions.





Pressure tester

2. Get a second person to actuate the starter. The test for this cylinder is complete once the test equipment's pointer stops climbing. Keep the accelerator pedal fully depressed.
3. Deflate the pressure on the test equipment. Observe the operating instructions for the equipment.
4. Move the scale on to another cylinder. To do this, pull the pin once under the handle on the back.





Moving test equipment on by one cylinder

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

Subsequent work

1. Fit spark plugs.
2. Fit the fuses for the ignition rod modules and the injection system.
3. Fit lid of central electric box. -arrows-





Central electric box

4. Read out the fault memory and erase it if necessary.