Models with 2.8-liter 6-cylinder engine
To combine one with the other, Audi engineers have developed a new intake manifold with a variable path length. Depending on the operating modes, six shutters close and open inside it. In this way, for each cylinder, an intake manifold of different lengths with different cross-sections is provided, or an intake manifold for torque (long pipe with small diameter), or power intake manifold (short pipe with large cross section).
All six dampers are vacuum-actuated and speed-controlled: up to 4000 rpm they remain closed to achieve high torque. Above 4000 rpm, they open fully to achieve high 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 develops its maximum torque of 245 Nm at 3000 rpm with the use of AI-95 gasoline; with the use of AI-98, its torque rises to 250 Nm. In the range from 2000 rpm to 5500 rpm, a torque of at least 220 Nm develops.
Checking the operation of the intake manifold with a variable path length
Start the engine and bring the speed to over 4000 rpm.
Observe the intake manifold diaphragm switch mechanism: the actuator rod should now move back.
If this is not the case, check the vacuum hoses for leaks. If they are ok:
Check the membrane mechanism: put a spare vacuum hose on the connection of the mechanism, firmly pull it in with your mouth.
If the rod does not move and / or a lot of air is drawn in, the membrane mechanism is faulty. Replace. If the mechanism is ok.
Check variable intake manifold changeover valve: remove both vacuum hoses from the valve. Attach the spare vacuum hose to the tip to the valve inlet tube.
Strongly draw in the mouth of the air from the spare vacuum hose. Air intake should be impossible (obstruction).
Start the engine, bring the engine speed to well over 4000 rpm.
Again, strongly draw in the air with your mouth. Air intake should now be possible (patency).
If so far you have not been able to find where the malfunction is hiding (which in itself is incredible enough), then the workshop should deal with the control check.
Remove engine protection.
The 2.6-liter 6-cylinder engine does not have a variable intake manifold. Its intake manifold consists of the parts shown in the figure. When designing, particular importance was attached to the low weight of the collector.
Removing the variable intake manifold with a 2.8-liter 8-cylinder engine
Remove the tips of the spark plugs, remove the high-voltage wires from the holders.
Remove the fuel distribution line together with all injection nozzles.
Remove air intake hose.
Remove idle speed control valve or disconnect plug.
Remove all vacuum/crankcase breather hoses at intake manifold and throttle body.
Remove cable «gas» and throttle potentiometer plug.
Loosen the bolts in the opposite order to that shown in the figure below on the right.
Remove intake manifold with throttle body.
Installation: Replace gaskets.
Tighten the intake manifold mounting bolts according to the sequence shown in the illustration below in four stages.
First stage: 5 Nm, second stage: 10 Nm, third stage: 20 Nm, fourth stage: again 20 Nm.
Withdrawal (with 2.6 liter 6-cylinder engine)
Logically, the removal process is identical to that of the 2.8-liter engine.
For the tightening sequence of the mounting bolts, use the same as for the 2.8-liter engine.
The intake manifold fixing bolts for the 2.6-litre and 2.8-litre 6-cylinder engines must be tightened in the sequence shown in the figure below. This is the only way to prevent distortion of the intake manifold during installation. The illustration on the left shows the same mounting bolts once again in the engine.
Visitor comments