Intake manifold

The intake manifold distributes the filtered charge air compressed by the turbocharger in a controlled manner to the individual cylinders. The geometry of the intake ports, internal volume, flange fitment and connections for sensors, EGR lines and charge-air pipes directly determine cylinder filling, combustion and emission values. For MAN and Mercedes trucks, buses and vans, the intake manifold is therefore not a universal cast or plastic part: design, port layout, pressure and temperature resistance differ according to engine family, emission standard and vehicle application.

Intake manifolds are available in cast aluminium, cast iron and heat-resistant glass-fibre-reinforced plastic. Cast versions are robust under high thermal loads, while plastic manifolds offer a weight advantage but are more susceptible to hairline cracks, warped flanges and damaged hose connections. On turbocharged engines, the manifold must withstand the pulsations and boost pressure of the charge-air system; sealing surfaces, O-ring grooves and mounting points must also remain dimensionally stable.

For MAN D08, D20, D26 and D38 engines, manifolds differ according to displacement, EGR configuration, turbocharger layout and the location of pressure and temperature sensors. At Mercedes, there are clear differences between older OM 364, OM 366 and OM 442 engines and electronically controlled Euro engines such as OM 457, OM 460, OM 471 and OM 473. The OM 501 and OM 502 V-engines also use specific intake systems with a different cylinder-bank layout, manifold shape, connection flanges and air distribution than inline engines. Always identify an intake manifold using the vehicle chassis number. Visual comparison or selection based solely on the model name is never sufficient.

A leaking or contaminated intake manifold often causes loss of power, increased fuel consumption, black smoke under load, irregular idling or fault codes relating to boost pressure, air mass or intake-air temperature. On engines with exhaust gas recirculation, soot and oil mist from the crankcase ventilation system can build up in the intake ports. This reduces the effective flow cross-section and causes differences in cylinder filling between cylinders. Cracks around mounting lugs, sensor sleeves, EGR connections and hose connections regularly occur due to vibrations, thermal cycles and excessive mounting forces.

First inspect the air filter housing, turbocharger intake hose, charge-air cooler, pressure pipes and hose clamps; a fault outside the manifold can cause identical symptoms. Then perform a pressure test on the charge-air circuit using a suitable blanking adapter and regulated compressed air. Test only within the system pressure specified by the manufacturer. Locate leaks with leak-detection spray or a smoke tester, paying particular attention to gasket surfaces and plastic weld seams. Using a diagnostic tester, compare the requested and measured boost pressure, intake-air temperature and air-mass values during a load test. A persistent pressure difference without a leak may indicate internal contamination, a faulty EGR control valve or a turbo system problem.

Remove the intake manifold only after residual boost pressure has been released and open intake ports have been carefully protected against dirt. Check the flatness of the cylinder-head sealing surface using a straightedge and feeler gauge; local distortion, corrosion or embedded material will cause renewed leakage even with new gaskets. Replace gaskets, O-rings, damaged mounting bolts and deformed hose clamps in accordance with the specified tightening torques and tightening sequence. Clean EGR passages and sensor connections without allowing loose carbon deposits to fall into the cylinder head.

After installation, fault codes must be cleared, the charge-air system must be checked again for leaks and a road test under load should follow. In addition to technical support with identification, Braem can help match new, used or reconditioned components to the correct vehicle configuration.