Sooting of intake ports of diesel engines

Sooting can occur in the intake area due to the entry of oil (via the crankcase ventilation) and soot (via the exhaust-gas recirculation) into the drawn in fresh air. In such case, the cross-section of the intake area is severely reduced which has a correspondingly negative impact on the air mass flow.

Consequences and diagnosis

Consequences of sooting

The following notable consequences may occur when sooting is present:
  • Rough engine running.
  • Engine jerks.
  • Engine delivers no power.
  • Various faults can be stored in the engine control unit.

Possibilities for diagnosis in case of sooting

An unambiguous check of the intake area for sooting can only be carried out by means of a visual inspection. Along with the relative fault code entries, the functional checks mentioned below can however provide certain indications of sooting.

Above all, the following three points may indicate sooting:

  • Engine speed variations at higher engine speeds.
  • Behaviour of the air mass measured by the hot film air mass meter at higher engine speeds.
  • Behaviour of swirl flaps in closing action (only in engine versions with swirl flaps).

The intake area can be checked for sooting by means of the following three functional checks:

  • Engine speed variation functional check.

    The engine speed is increased automatically in stages. If the intake area is sooted, the air supply and thus combustion deteriorate, leading to less smooth running. The higher the engine speed, the more the effect is noticeable. Conversely, a sooted intake area has no effect on smooth running in the idle range.

  • Air mass deviation functional check.

    The calculation of the air mass flow in the engine control unit is falsified by the reduction of the intake area's cross section. The resulting deviation between the measured air mass and the calculated air mass can be detected by means of the functional check of the hot film air mass meter. If the intake area is sooted, the measured air mass falls below the calculated value. The higher the engine speed, the greater the effect.

  • Function check, swirl flaps

    Note: Swirl flaps are not installed in the following engine versions:

    • N47 in MINI with the exhaust emission standards European version 3, 4 or 5.
    • All N47 with low performance class.

    The dynamic behaviour of the swirl flaps gets worse if the intake area is sooted. Especially the closing action of the swirl flaps shortly before the closed condition is reached is significantly slower. This can be detected in the functional check by the fact that the position of the swirl flaps follows the activation value with a delay.

Cleaning in case of sooting

If intake area sooting has been discovered, the intake area can be repaired by cleaning.

Procedure in accordance with repair instructions 11 12 800.

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