Cold Running / Starting Problems

Engine starts, runs, then stops
Engine starts, but idles roughly when cold
Engine smokes excessively and/ or misses when cold
Engine is hard to start; cranking time is too long

Diagnosis Procedure

  • Check for correct starting procedure
    A cold diesel engine will not start and run properly if the correct starting procedure is not followed. It is important that the glow plugs are allowed to complete their glow cycle and that the cold start timing advance is used. Both of these items help to overcome the loss of compression heat in a cold engine.
  • Check the fuel supply system
    Loose connections or cracked hoses between the fuel tank and the injection pump will allow air to enter the fuel system. The air then becomes trapped in the fuel system and can cause the engine to run roughly, stall, or smoke excessively.

    The union bolt on the return fuel line from the injection pump has a restriction to help maintain adequate fuel pressure in the injection pump. If this bolt is placed in the inlet side or the incorrect bolt is used, the injection pump will not develop enough pressure, and the car will not run properly.
    In areas where the temperature drops below 20°F (-7°C), the fuel tank strainer- should be removed to prevent wax crystals from blocking the fuel supply. This is only necessary on the Rabbit, Jetta, Pick-up, and Dasher. Other 4 cylinder diesels do not use a fuel tank strainer.

  • Check the glow plug system
    During cold starts, the compression heat is dissipated by the cold engine. If the glow plugs are not operating properly, the engine may start, but run roughly and/or smoke. This could be caused by temperatures being too low in the swirl chambers where the glow plugs are located.