just a quick question. does the n75 hold pressure to the DV's or do they default closed, then open when u let off the throttle.

so if the pressure to the DV's is incorrect they could leak boost?

i just did a boost leak test (marks method from the turbos) and no leaks but the pressure was going somewhere because my compressor had to charge(80 gallon), but there were no visible or audible leaks. test was done at about 18 to 20 lbs.

reason for the question is that i think i might have a bad n75.
thanks

 

n75 valve would controll the wastegates, the n249 valve ( called in the audi scene) would controll the DV's

 

You didnt find the leak... your thinking to much about it... spray water and soap all over.. get someone to help...if you cant find it.. take out the Y pipe and do it from there... 3" couplers is required... block off the one hose going to Y pipe...
I post some pics of my weekend issue... it was the TB seal leaking on a clients car...

 

I figured i was thinking quite far about this one. But after no leak found I wondered, where else could it go

When I did it the whole engine bay and the turbos and the wastegates were covered in soapy water.

Maybe there is no leak but my boost request is quite high and I feel the request could be covering a problem.

The car has 16/24 turbos 5bar and the request is 80 %. I also have 1bar wastegates that are adjusted. My tuner tells me that is high and I should be getting more then I am. I am at 1.0 to 1.1(when it's cool outside).

I will not say any names(they are very knowledgable, I feel I am the one lacking the knowledge and I'm far from stupid.)

I just don't want my tuner to have to over work due to my lack of correctly operating equipment or cover for a problem and over work the turbos.

So that leads back to the question. Does the n75 control the DV's. And does the dv's default closed or does positive air pressure keep them closed. (the later part makes sense to me.)

Thanks

 

subscribed.

 

IM lost.. what do you mean by 80%

your thinking to much about it...
the last two cars were OEM and both had OEM parts fail... check valves .. now the TB O ring.. which took me 6 hours to find... took everything apart... that was a *****...
Im going to start a thread.. common things I find on clients cars... you will be shocked..
markski

 

As was said earlier (post #2) ...N75 ONLY controls wastegates....DV's could be leaking too...Are they new? Aftermarket? Do exactly whatever Markski tells you to do and you will be fine.

 

They are fairly new 4 months old. They are agency powers.

 

Check them anyway...I've seen brand new ones leak. Most use the 710N....upgraded factory Audi DV's...cheap and work very well....

 

do a pressure test at the TB,.. 20 psi...

 

What am I isolating at that point. And thanks for the info

 

I would need to take a manual and probably spend an hour explaining...
its the first tear boost leak test.. second is at the turbos...
this is how we do it... and it works... good luck..

 

Useful thread! Subscribed.

 

To answer one question (at least from an Audi S4 owner) The DVs are open, (or partially) until you press the gas and the ECU sees you want to build boost. Then obviously they open again when you let off the gas to vent (or divert) but they are not "always" closed like a blow off valve. Since they recirculate, you can't hear when they are open, and since it's a closed loop, it's not a "leak" per se, they are open far more than you would think (not just during a shift) I'm convinced this constant cycling of the DVs, combined with the N75 control of the wastegates and the fly by wire throttle is why the Audi feels soft and somewhat sluggish in boost response compared to a more typical turbo charged tuner car.

 

Thats one of the reasons i deleted my N249 valve, I have also been using a MBC only tune with no N75 valve in the car at all. You describe it well, The car feels sluggish in boost in the factory config. My car feels a bit harsh, on/off boost.