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How do you check the vac system on these cars? I've got a vac gauge, can i tee that in and see if its holding the vacuum? do run the car and build the vac then stop the car and see if it drops or how fast it drops.?

See if it can pull a steady and repeatable reading at idle. I'd expect even on a healthy car it'll tail off very quickly once the car is shut off.

Im thinking of running it into the car and seeing what happens under load. Any idea the best place to tee in?

These cars have a unique system
They do not rely on engine vacuum
They have an electric pump and a venturi across the throttle body

I have no idea what values to expect under what operating conditions
Perhaps try when idling and under load

Google 'audi rs4 training pdf' see if it comes up
Has a description of the system but is not a Shop manual

A better approach may be to locate a known main vacuum line
T into it with engine off and see what you can pull with a hand pump (like used for brake bleeding)
Should tell you if you have leaks, should hold a vacuum
If it bleeds off you may have a leak

ArthurPE wrote:These cars have a unique system
They do not rely on engine vacuum
They have an electric pump and a venturi across the throttle body

I have no ida what values to expect under what operating conditions
Perhaps try when idling and under load

Google 'audi rs4 training pdf' see if it comes up
Has a description of the system but is not a shop manual

A better approach may be to locate a known main vacuum line
T into it with engine off and see what you can pull with a hand pump (like used for brake bleeding)
Should tell you if you have leaks, should hold a vacuum
If it bleeds off you may have a leak

I think the manual was also called the self study.

Apologies, there training guide is different:
http://www.ibiblio.org/tkan/audi/RS4_Training_Guide.pdf

This is the self study:
http://www.volkspage.net/technik/ssp/ssp/SSP_377.pdf

MikeFish wrote:

ArthurPE wrote:These cars have a unique system
They do not rely on engine vacuum
They have an electric pump and a venturi across the throttle body

I have no ida what values to expect under what operating conditions
Perhaps try when idling and under load

Google 'audi rs4 training pdf' see if it comes up
Has a description of the system but is not a shop manual

A better approach may be to locate a known main vacuum line
T into it with engine off and see what you can pull with a hand pump (like used for brake bleeding)
Should tell you if you have leaks, should hold a vacuum
If it bleeds off you may have a leak

I think the manual was also called the self study.

You are correct sir
http://www.tbfh.org/wp-content/uploads/ ... yGuide.pdf

You could use VCDS and run the power flap and manifold flap tests - details in the FAQs thread. If the flaps don't actuate then usually there is a vac leak.
Also check the rear exhaust flaps close on idle with sport off as this needs vacuum to close.

MikeFish wrote:Apologies, there training guide is different:
http://www.ibiblio.org/tkan/audi/RS4_Training_Guide.pdf

This is the self study:
http://www.volkspage.net/technik/ssp/ssp/SSP_377.pdf

thanks,

bit of light bed time reading for me i think...

PaulT wrote:You could use VCDS and run the power flap and manifold flap tests - details in the FAQs thread. If the flaps don't actuate then usually there is a vac leak.
Also check the rear exhaust flaps close on idle with sport off as this needs vacuum to close.

hopefully going to do that tomorrow...

http://www.jlosee.com/images/RS4/PDF/TS ... fold-1.pdf

Is this what you're looking for?

ashleyg wrote:http://www.jlosee.com/images/RS4/PDF/TS ... fold-1.pdf

Is this what you're looking for?

That's a great help... Thanks

On mine the relay that controls the vacuum to the power flap had rotted and was leaking the vac so both maniflod flaps and power flaps were not opening. This relay is low down under the airbox so not the cleanest driest place so rotting is not a big surprise IMO.

The vac line to the left from the double T at front of engine goes to the power flap only. So if you suspect the power flap relay then you can remove this line and plug the open end of the T. This isolated the leak for me and manifold flaps were then working. Replaced the rotted relay and was then all ok.

PaulT wrote:On mine the relay that controls the vacuum to the power flap had rotted and was leaking the vac so both maniflod flaps and power flaps were not opening. This relay is low down under the airbox so not the cleanest driest place so rotting is not a big surprise IMO.

The vac line to the left from the double T at front of engine goes to the power flap only. So if you suspect the power flap relay then you can remove this line and plug the open end of the T. This isolated the leak for me and manifold flaps were then working. Replaced the rotted relay and was then all ok.

i supose in a way finding something like this is nice in that it's a clear cut failing.
Now you've got the vac all sorted, what happens if you remove the oil filler cap whilst the car is running.

Pop one of the hoses off the 4mm vacuum lines that lay under the front carbon fibre trim in the engine bay.
If you take the car for a run, and then stop the engine, pop the hose off, and theres no hiss as the vacuum is lost, then you have a substantial vacuum leak.

A good system should hold for 5+ minutes after the engines turned off.

My money would be on the check valve under the inlet manifold. Only accessible while the manifolds off.
If youve just had a carbon clean, it would have been the ideal opportunity to change it out.

I had a decent vacuum leak and when i had my last carbon clean, i asked for that valve to be replaced.
After the carbon clean, i did as described earlier and it still had vacuum over ten minutes after the engine was off.