Possibilities for diagnosis in case of sooting

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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.
Behavior of the air mass measured by the hot film air mass meter at higher engine speeds.
Behavior of the swirl flaps during closing action.

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.
Functional check of the swirl flaps (not for N47 in MINI with exhaust emission standards Euro 3, Euro 4 or Euro 5). The dynamic behavior 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.