Aspiration intake

The air intake duct forms the first section of the air intake system between the external air inlet and the air filter housing. On MAN and Mercedes trucks, buses and vans, this plastic or metal air duct guides the intake air in a controlled manner to the air filter unit, often via an integrated water separator, coarse debris separator or intake scoop. A correctly fitting air intake duct is essential to supply the engine with sufficient clean, cool air and to keep dust, spray water, leaves and other contaminants out of the intake system. The correct part must always be identified using the chassis number; visual comparison or selection based solely on the model name is never sufficient.

Air intake ducts vary considerably according to cab variant, vehicle series, wheelbase, emissions standard, bodywork and the position of the air filter housing. For example, a MAN TGL with a D08 engine generally has different air routing from a TGX with a D26, D38 or D20 engine. Mercedes versions also differ between vehicles with OM 904, OM 906, OM 457, OM 471 or OM 473 engines. The air intake of a Mercedes Atego, Axor, Actros, Citaro bus or Sprinter is furthermore tailored to the available installation space, the engine's air demand and the position of the cab, mudguard and air filter housing.

The parts are generally made from impact-resistant thermoplastic materials, such as polypropylene or polyamide, optionally reinforced with glass fibre. These materials must withstand vibrations, temperature fluctuations, UV exposure, road salt and cleaning agents. Pay attention to the correct diameter, oval or rectangular cross-section, installation angle, sealing lips, mounting points and connection to resonators or pre-filters. Even minor deformation, a missing clip or an incorrect fit may result in unfiltered air intake or increased intake resistance.

Common faults include hairline cracks around mounting lugs, worn mounting clips, torn sleeves, disconnected joints and deformation caused by collision damage or contact during cab tilting. On vehicles frequently operated on unpaved terrain, the air intake duct may become internally contaminated with dust, leaves, mud or snow residue. This restricts the effective flow cross-section and increases the vacuum upstream of the air filter. Possible consequences include loss of power, increased fuel consumption, more frequent particulate filter regeneration and fault messages relating to air mass or turbo pressure.

First inspect the entire route from the intake grille to the air filter housing using a lamp and mirror. Specifically check seams, bends, sealing edges and mating surfaces for cracks, abrasion marks and leak paths. Then check whether the air filter housing closes correctly and whether the filter seal has been bypassed by dust traces. Clear dust deposits downstream of the air filter element indicate a leaking filter seal, damaged housing or incorrect installation; the air intake duct itself should then also be assessed for damage.

If in doubt, measure the intake restriction using a vacuum gauge or differential pressure gauge at the specified measuring point upstream of the turbocharger. Compare the measured vacuum at increased engine speed and load with the factory specification. Also read the live data: air mass meter values, turbo pressure, intake air temperature and the plausibility between requested and actual boost pressure help distinguish between an obstruction in the air supply, a contaminated air filter, a leaking charge air pipe or a faulty sensor.

Replace an air intake duct if it has cracks, missing mountings, permanent deformation or insufficient sealing. Repairs using tape, sealant or universal hoses are unreliable: the material must retain its shape under vibration and vacuum and must not create an unfiltered bypass. When replacing it, also clean the air filter housing, water drain and any pre-filter. Only install suitable clamps, rubber mounts and sealing rings, and after installation check that the duct is clear of sharp bodywork parts. Braem can assist with the technical identification of new, used or reconditioned components based on the chassis number, helping to minimise downtime and consequential damage to the turbocharger and engine.