2.8L six-cylinder engine
High engine torque, even at low speeds, is provided by a long intake manifold with small diameter pipes. To ensure high engine power at high speeds, on the contrary, a short intake manifold with large diameter pipes is required.
To connect these two approaches, AUDI has developed a reconfigurable intake manifold. In the pipes of this intake manifold there are six dampers that close and open depending on the load on the engine. Thus, each cylinder has at its disposal an inlet pipe of different lengths and diameters, which can be referred to as an inlet pipe for maintaining high torque and an inlet pipe for developing engine power characteristics. The dampers in the intake manifold pipes are actuated by low pressure air depending on the engine speed. Up to 4000 rpm, they are in the closed position, providing the engine with high torque. When the engine speed exceeds 4000 rpm. dampers open fully.
If the effective power of the engine drops, it is necessary to check the functioning of the dampers in the intake manifold pipes.
1. First check the ease of movement of the damper rods.
2. Check the operation of the shutters. This check is performed with the engine warm.
3. Start the engine and raise its speed above 4000 rpm.
4. Watch the membrane valve for switching the dampers of the intake manifold pipes. The damper rod must move back. If not, check the condition of the low air pressure hoses and make sure they are tight. If so, then:
5. Check diaphragm valve. To do this, attach a spare hose for low air pressure to the valve connection and suck air out of the hose with your mouth. If, in this case, the intake manifold damper rod does not move, or air is constantly in the hose, despite attempts to pump it out by mouth, then the diaphragm valve is faulty and must be replaced. If the diaphragm valve is normal, then check the valve for sequential reconfiguration of the cavity of the intake manifold pipes. This valve is located next to the intake air mass meter at the rear of the engine on the right side. This valve determines if low air pressure is required for the diaphragm valve (see illustration).
6. Disconnect the two low air pressure hoses from the intake manifold cavity reconfiguration valve (see illustration). Fit a spare low pressure air hose to the valve port leading to the intake manifold.
7. Suck in air from this hose. Air must not pass through the hose.
8. Start the engine and bring the speed to 4000 rpm and above.
9. Suck in your mouth air from the hose. Air should now flow through the hose. If the defect could not be established, which is unlikely, then contact the workshop.
Withdrawal
10. Remove the protective cover over the motor.
11. Remove the tips of the spark plugs, and release the high voltage wires from the holders.
12. Disconnect a distributive fuel line together with atomizers.
13. Disconnect the air intake hose.
14. Remove the idle speed stabilization valve or disconnect its plug.
15. Disconnect all low pressure hoses from the intake manifold. Also remove the hose from the throttle valve and the crankcase breather hose.
16. Disconnect the cable «gas» and plug for throttle angle potentiometer.
17. Turn out bolts of fastening of an inlet collector. The sequence of unscrewing the bolts is opposite to their tightening (see illustration).
18. Remove the intake manifold along with the throttle body.
Installation
19. Replace old gaskets with new ones.
20. Tighten the intake manifold mounting bolts in the sequence shown in illustration 8.17. Tighten the bolts in four passes with the following torques:
1st stage: 5 Nm;
2nd stage: 10 Nm;
3rd stage: 20 Nm;
4th stage: 20 Nm.
Attention! Removal and installation of the intake manifold of the 2.6-liter six-cylinder engine are carried out identically. The moments and order of tightening the manifold mounting bolts are the same as for the 2.8 liter engine.
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