COMPRESSION PRESSURE CHECK


1.Before inspection, check that the engine oil, starter and battery are normal. In addition, set the vehicle to the pre-inspection condition.
2.Turn the ignition switch to "LOCK" (OFF) position.
3.Remove the EGR pipe.
4.Remove all of the glow plugs.

5.Disconnect the injector connector of all cylinders.
note Doing this will prevent carrying out fuel injection.

6.Cover the glow plug hole with a shop towel etc., and after the engine has been cranked, check that no foreign material is adhering to the shop towel.
caution
  • Keep away from the glow plug hole when cranking.
  • If compression is measured with water, oil, fuel, etc., that has come from cracks inside the cylinder, these materials will become heated and will gush out from glow plug hole, which is dangerous.
  • If deformed or damaged due to the repeated use, the gasket must be replaced with the new special tool, gasket kit MB992352.

7.Set the compression gauge to one of the glow plug holes. If the compression gauge interferes with the fuel injection pipe No.1, perform the following services:
(1) Remove the fuel injection pipe No.1.
(2) Set Special Tool Common Rail Plug (MB9922346) to the fuel injection pipe No.1 installation hole of the common rail Assy.
8.Crank the engine and measure the compression pressure.

    Vehicles without variable geometry turbocharger:
    Standard value (at engine speed of 250 r/min): 2,500 kPa
    Limit (at engine speed of 250 r/min): min. 1,750 kPa

    Vehicles with variable geometry turbocharger:
    Standard value (at engine speed of 150 r/min): 2,400 kPa
    Limit (at engine speed of 150 r/min): min. 1,650 kPa
9.Measure the compression pressure for all the cylinders, and check that the pressure differences of the cylinders are below the limit.
Limit: max. 300 kPa
10.If there is a cylinder with compression or a compression difference that is outside the limit, pour a small amount of engine oil through the glow plug hole, and repeat the operations in steps 7 and 8.
(1) If the compression increases after oil is added, the cause of the malfunction is a worn or damaged piston ring and/or cylinder inner surface.
(2) If the compression does not rise after oil is added, the cause is a burnt or defective valve seat, or pressure is leaking from the gasket.
11.Turn the ignition switch to "LOCK" (OFF) position.
12.Remove the special tool, common rail plug (MB992346).
13.Install the fuel injection pipe No.1 (Refer to GROUP 13, Diesel Fuel - Fuel Injector and Common Rail - Removal and Installation).
14.Connect the injector connector of all cylinders.
15.Install the glow plugs.
Tightening torque: 17 ± 2 N·m
16.Install the EGR pipe.


17.Use the M.U.T.-III to erase the diagnosis codes.
note This will erase the diagnosis code resulting from the injector connector being disconnected.