101902 Performing Compression Pressure Check on DFI Engines
WM 101902 Performing compression pressure check on DFI engines
Tools
Preliminary work
1. Open the bonnet.
2. Open lid of central electrics box. To do this, loosen the four fastening screws. -arrows-
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. Pull out the fuses for the ignition rod modules and the injection system. For latest assignment, see wiring diagram.
4. Remove spark plugs. -> 287020 Removing and installing spark plugs on DFI engines - section on "Removing" Service and Repair
Tools and materials
Tools
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 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 localisation 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.
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. -> 287020 Removing and installing spark plugs on DFI engines - section on "Installing" Service and Repair
2. Fit the fuses for the ignition rod modules and the injection system.
3. Fit lid of central electrics box. -arrows-
Central electrics box
4. Read out the fault memory and erase it if necessary.