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Your Inlet Manifold (Intake Manifold) worn out? » Read more about common malfunctions • Repair • Replacement manual
Distribute air with the intake manifold
The intake manifold, sometimes also referred to as the "inlet manifold", is a component that distributes the intake air to the individual combustion chambers within the cylinder head. The intake manifold has to endure the engine's vibrations, high temperatures and possible also high pressure. This makes it a highly stressed component. Since inlet manifolds consist of a thermostable plastic specifically tailored to each type of vehicle, replacement parts usually cost several hundred euros.
The path of intake air
For an engine to constantly perform within the optimum range of combustion, a precise dosage of fuel is needed with the present intake air. The air flow meter built into the intake tract permanently informs the control unit of the exact amount of intake air. The control unit uses this information to calculate the existing atmospheric oxygen, according to which it injects the optimal amount of fuel. For this reason, it is very important that the quantity of intake air does not change between the air flow meter and the cylinder head. Leaks in the intake tract always lead to malfunction. The path of intake air is as follows: Air filter housing, air flow meter, in some cases charger, charge air hose, intake manifold, intake gasket, cylinder head. The intake manifold is one of the highest-quality components in this sequence.
Repairing the intake manifold
An intake manifold is made of plastic. While this saves weight, it also slightly limits the life of this component. In cars featuring a turbocharger, G-charger or supercharger, the intake manifold is further stressed by the high internal pressure. Vibrations from the engine, the internal pressure and fluctuations in temperature put a real strain on this component. The screw connections on the cylinder head are particularly critical. As these weak points are inevitable due to the nature of their design, they are particularly prone to breakage during replacement of the intake manifold gasket. Depending on the type of vehicle, risk of damage to this component becomes increasingly likely in vehicles with a mileage exceeding 150,000 km.
With older vehicles, which will likely be disposed of in a matter of months, a temporary repair of the intake manifold with epoxy resin or heat-resistant glue may be attempted. Such patched measures are not recommended for vehicles intended to remain in operation for a few more years, as there is a risk of such a makeshift repaired area tearing back open and once again restricting the vehicle's performance. Thus, exchanging the defective intake manifold with a new part is usually the only option. Precisely determining defects The intake tract is designed in such a manner, that the intake manifold is usually the last component to break. Suction hoses, intake gaskets and even air flow meters are usually significantly cheaper than an inlet manifold. Usually, they will become defective first. If an engine behaves as if it is drawing leakage air, it is useful to examine the entire tract. Initially, the entire intake tract should be inspected for leaks with the engine running. Leaks can reveal themselves through hissing or whistling noises. A lit cigarette or some incense can also point to a leak, if unusual air turbulence is observed. If this method does not yield success, one can continue to look for the leak by spraying short bursts of brake cleaner on the intake tract. The leak will be revealed by a change in the motor speed. The intake manifold gasket and the bellows in the suction hose are usually affected by wear first. Therefore, the search for a leak should begin with these components.
If the intake system must be removed, the inside should also be inspected for oil deposits. Depending on the engine type, a light film of oil may be normal, as the engine ventilation may be connected to the intake tract. If, however, the oil is already leaking out as a trickle, a larger defect exists. This drag-in of oil should be remedied prior to repairing the intake tract. With a little luck, the cause might simply be too much engine oil being refilled. In the worst case, the piston rings are leaking, which requires a serious engine rebuild. If large amounts of oil are found in the intake tract, the intake manifold and the air flow meter must be thoroughly cleaned prior to reinstallation. Gasket and suction hose must also be replaced in this case as a precaution, since oil decomposes both parts from the inside. Quality of brand-name inlet manifolds Intake manifolds are highly specific components, which only fit a specific type of engine. Thus, usually only OEM manufacturers supply these components. This, however, ensures that the customer receives the maximum quality of this part, which will have the same service live as the original part had.