Vacuum Unit - when is a vacuum pipe necessary?

[geoffreytro]

charge pressure control.jpg
The charge pressure control solenoid valve (3) to the Non return valve (4) has a tube (7). In my car (Audi 2.5tdi BFC V6) the tube was cut and both cut ends tucked behind the fuel filter. I have replaced the cut tubes with one complete tube (consistent with the diagram).

Does if matter? The non return valve side (4) was probably okay. Not as sure about the charge pressure control solenoid valve.

[Crasher]

DO you mean the pipe to the air filter?

[geoffreytro]

No, the pipe to the air filter is number 2 in the diagram on the origional post. Its the tube from the non return valve (thats black and white and has to be fitted the correct way round) to the pressure control solenoid valve. Thats 3 and 4 on the diagram.
Thanks for the interest
G

[Crasher]

Well I would say it must be a the diagram says, which year and engine code is your car? Does the N75 valve have a vacuum feed?

[geoffreytro]

Engine code BDG 2004, yes tube goes from the pressure control solenoid to the vacuum unit (tube 1 on diagram).
Query comes from my surprise that someone would cut tube 7, and I wondered was there a rational reason and was I wise to repair it. It's a circuit that I don't really understand the principles.
As you advise, if it's in the diagram - it must be right!

[Crasher]

The one way valve allows the vacuum pump (6) to create a vacuum in the light grey line and this provides the N75 (3) and the N18 EGR solenoid with a strong vacuum, the one way valve prevents the vacuum pump allowing the depression to deplete when the engine is off. The N75 then uses this vacuum signal in a modulated on/off fashion to apply a vacuum to the turbo control diaphragm which alters the position of the internal vane ring and allows the engine ECU to position the ring exactly where it wants it to be according to the map in the memory. The other line from the N75 is the vent line for the N75 and the N18 and the go to the air filter in order to provide them with clean air without having to resort to a separate filter.

1	Vacuum hose From EGR valve -N18- to mechanical EGR valve
2	Mechanical exhaust gas recirculation valve
3	To solenoid valve for charge pressure control -N75-
4	Vent hose to air cleaner housing Depending on version
5	Non-return valve Note installation position (light side/dark side) - as shown in illustration
6	Brake servo
7	Exhauster pump
8	Exhaust gas recirculation valve -N18-
9	To vacuum reservoir
10	Throttle butterfly valve -N211- Depending on version
11	To intake manifold flap Depending on version

[geoffreytro]

Thanks for your advice. This is one of the final stages of an engine rebuild - few more parts to get and then its back on the road.

[Crasher]

Ahh, someone else who can't sleep.......