The 2.6L six-cylinder engine does not have a switchable intake manifold. Its intake manifold consists of the assemblies shown here. Here, special attention is paid to the low weight of the structure.
The flaps of the switching intake manifold with a six-cylinder engine with a displacement of 2.8 liters are actuated by a vacuum box (2) with a vacuum hose (1). This box should not be confused with the vacuum box (3) speed control systems (additional equipment).
Valve (1) register intake manifold switch determines whether there should be a vacuum in the vacuum box. It receives a signal to switch over the wire (2) from the injection control unit. Then the vacuum from the tube (3) the intake manifold may move towards the tube (4) vacuum box. The valve is installed behind the intake manifold on the so-called intake air silencer.
The photo shows the fixing bolts (arrows) intake manifold.
Shown here is the sequence in which the intake manifold mounting bolts are tightened for the 2.6L and 2.8L six-cylinder engines. This is the only way to avoid deformation of the intake manifold when installing.
Six-cylinder engine with a displacement of 2.8 liters
High torque even at low speeds is ensured by a long suction tube with a small diameter. On the contrary, a short suction pipe with a large cross-section is required to ensure high engine power at high speeds. To combine both, Audi has developed a switchable intake manifold. In it, depending on the situation, six shutters close and open. Thanks to this, each cylinder has at its disposal one of the suction pipes of different lengths and with different diameters: either an intake manifold to provide torque (long tube with small diameter) or intake manifold for power support (short tube with large diameter).
All six dampers are low-pressure actuated and controlled depending on the engine speed: up to 4000 rpm they are closed to provide high torque. Above 4000 rpm they are fully open to support power. Below 4000 rpm, up to 30 Nm of torque is gained with the intake manifold compared to the power intake manifold.
The 2.8 liter engine reaches its maximum torque of 245 Nm at 3,000 rpm using Euro-Super petrol (euro-Super); with super plus petrol (98 ROZ) torque rises to 250 Nm. A minimum of 220 Nm is available over a wide range from 2000 to over 5500 rpm.
Checking the function of the switching intake manifold
The intake manifold switch should only be checked if there is a lack of power. First, check with your hand the ease of movement of the lever mechanism. This is followed by a functional test: this is done with the engine warm:
1. Start the engine, raise the speed well above 4000 rpm.
2. Observe the vacuum box: the control rod must be pulled back.
3. If not, check the vacuum hoses for leaks. If they are ok:
4. Check the vacuum box: put the spare hose on the box connector, suck vigorously with your mouth.
5. If the control rod does not move and / or a lot of air can be sucked in, the box is faulty. Replace it. But if the box is in working order:
6. Check the intake manifold register shift valve: remove both vacuum hoses from the valve. Slide the replacement hose onto the valve inlet manifold connector.
7. Suck vigorously on the spare vacuum hose. Air must not be sucked in (no patency).
8. Start the engine, raise the speed well above 4000 rpm.
9. Suck the hose vigorously again. Now the air should be sucked in (patency is).
10. If so far the source of the fault has not been found (which is pretty incredible), then in the workshop you need to check the setting.
Removing the switching intake manifold
Six-cylinder engine with a displacement of 2.8 liters
1. Remove the engine cover.
2. Disconnect the spark plug connectors, remove the high voltage wires from the brackets.
3. Dismantle the fuel distributor pipe together with all injection valves (chapter MPI/MPFI injection system).
4. Remove the inlet hose.
5. Remove the idle speed stabilization valve or disconnect the connector.
6. Remove all vacuum/crankcase breather hoses from intake manifold and throttle body.
7. Remove the throttle cable and its potentiometer connector.
8. Unscrew the bolts in the reverse order of tightening in the photo above.
9. Remove the intake manifold with throttle body.
10. Mounting: Replace gaskets.
11. Tighten the intake manifold mounting bolts according to the sequence shown in the figure above in four steps. 1st stage: 5 Nm, 2nd stage: 10 Nm, 3rd stage: 20 Nm, 4th stage: again 20 Nm.
Removing the intake manifold V6 with a displacement of 2.6 liters
1. Dismantling is carried out in the same way as with an engine with a displacement of 2.8 liters.
2. The tightening sequence for the mounting bolts is the same as for the 2.8L engine.
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