Compression Pressure Check

Required Special Tools: 

• MB992744: Vehicle communication interface-Lite (V.C.I.-Lite)
• MB992745: V.C.I.-Lite main harness A
• MB992747: V.C.I.-Lite USB cable short
• MB992748: V.C.I.-Lite USB cable long
• MB991958: Scan Tool (M.U.T.-III Sub Assembly)
  • MB991824: Vehicles Communication Interface (V.C.I.)
  • MB991827: M.U.T.-III USB Cable
  • MB991910: M.U.T.-III Main Harness A (Vehicles with CAN communication system)

1. Before inspection, check that the engine oil, starter and battery are normal. Also, set the vehicle to the pre-inspection condition.
2. Remove all of the ignition coils and spark plugs. (Refer to INTAKE MANIFOLD ).
3. Disconnect the injector connector.
   WARNING: Keep your distance from the spark plug hole when cranking. Oil, fuel, etc., may spray out from the spark plug hole and may cause serious injury.
4. Cover the spark plug hole with a shop towel etc., during cranking. After the engine has been cranked, check for foreign material adhering to the shop towel.
   Fig 1: Identifying Injector Connectors

   Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
   Fig 2: Checking Engine Compression Pressure

   Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
5. Set compression gauge to one of the spark plug holes.
6. Cranking the engine with the accelerator pedal fully depressed, measure the compression pressure.

   Standard value (at engine speed of 200 r/min): 1,650 kPa (239 psi) 

   Minimum limit (at engine speed of 200 r/min): 1,150 kPa (167 psi) 

7. Measure the compression pressure for all the cylinders, and check that the pressure differences of the cylinders are below the limit.

   Limit: 100 kPa (15 psi) 

8. 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 spark plug hole, and repeat the operations in steps  5 to  7.
   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.
9. Connect the injector connector.
10. Install all of the spark plugs and ignition coils. (Refer to INTAKE MANIFOLD ).
    CAUTION: To prevent damage to scan tool (M.U.T.-III), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-III).
11. Turn the ignition switch to the "LOCK" (OFF) position and then connect scan tool (M.U.T.-III) to the data link connector. (Refer to DIAGNOSTIC FUNCTION ).
12. Use the scan tool (M.U.T.-III) to erase the diagnostic trouble codes. (Refer to DIAGNOSTIC FUNCTION ).
    NOTE: This will erase the diagnostic trouble codes resulting from the injector connectors being disconnected.
13. Select "Mode $0A" from "Special Function" of scan tool (M.U.T.-III). Check whether the permanent-DTC (PDTC) is stored or not. If stored, clear the PDTC. (Refer to DIAGNOSTIC FUNCTION ).