Section 2.2 Compression Pressure Test

Section 2.2
Compression Pressure Test

To do a compression test the fuel injector will need to be removed and the compression tester installed.‪

  1. Set the parking brake and chock the tires.

    Note: To do this procedure, coolant temperature must be between 70-95°C (158-203°F).



    To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked.‪



    To avoid injury from inhaling engine exhaust, always operate the engine in a well-ventilated area. Engine exhaust is toxic.‪

  2. Turn on the ignition key switch and run the engine until it reaches operating temperature.
  3. Shut down the engine.
  4. Remove the fuel injector. Refer to MBE 900 Service Manual (6SE9007), fuel system chapter.
  5. Insert the compression test adaptor (J–46386) into the cylinder head. See Figure "Installing the Connector" .
    Click to see this graphic in a separate window

     1. Bolt‪

     2. Hold–Down Clamp‪

     3. End Cover (constant throttle)‪

    Figure 1. Installing the Connector

    1. Make sure the smooth surface on the O–ring is pointing toward the test adaptor (J–46386).
    2. Install the hold–down clamp with the two prongs around the test adaptor. Turn the hold–down clamp (at the cylinder head) until the button in the base of the hold–down clamp is aligned with the locating element in the end cover of the constant throttle valve end cover.
    3. Tighten the hold–down clamp bolt to 35 N·m (26 lb·ft).

      Note: Follow the equipment manufacturer's operating instructions to connect the compression tester.

  6. Attach the compression tester (J–6692–B) to the test adaptor (J–46386) . Thread the fitting at the end of the tester to the top of the test adaptor. See Figure "Testing Compression Pressure" .
    Click to see this graphic in a separate window

     1. Hold–Down Bolt‪

     3. End Cover (constant throttle)‪

     2. Hold–Down Clamp‪

     4. O–ring‪

    Figure 2. Testing Compression Pressure

Test as follows:‪

  1. Remove either of the electrical connectors from the MCM. When this is done, the engine will not start.
  2. For each cylinder, use the starter to crank the engine at least 8 engine revolutions. The results will be recorded on the gauge of the tester.
  3. Compare measurements on the gauge with the values listed in Table "Compression Testing" .


    Pressures kPa (psi)‪

    Compression Pressure at Starter Speed‪

    2800 (406)‪

    Permissible Difference Between Individual Cylinders‪

    400 (58)‪

    Table 5. Compression Testing
  4. If the pressure measured is below the chart compression pressure or above the permissible difference, determine the cause and correct the problem.

Install the fuel injector as follows:‪

  1. Disconnect the compression tester from the test adaptor. See Figure "Testing Compression Pressure" .
  2. Remove the compression test adaptor. See Figure "Installing the Connector" .
  3. Install the fuel injector. Refer to MBE 900 Service Manual (6SE9007), fuel system chapter.
  4. Repeat this procedure for each cylinder.
  5. Connect the MCM.
  6. Connect diagnostic tool to the vehicle and clear all inactive fault codes.
  7. Remove the chocks from the tires.

EPA07 MBE 900 DDEC VI Troubleshooting Guide - 6SE580
Generated on 10-13-2008

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