B5 S4 Boost question...
 

OK... So I got my new AWE center vent boost guage... Which is amazing...

But... I think I have a problem with my boost... When I push WOT My boost never goes straight to 17 psi how the GIAC says it should... First it goes to 15 and then creeps up to 17... On lower gears like 1st 2nd and 3rd it barely ever goes up to 17... lucky if 15...

When Cold underWOTit jumps to 15 then drops to 10...

Sometimes on WOTit goes up to 17 and then right awaydrops to 10 or 12 then pops up to 15 and creeps to 17 all on WOT... This is most noticable in 4th 5th and 6th gear...

Another thing... What is the vacumm supposed to be??? Mine is about 12-14 hg or sumthing... When i'm in a gear and not on the throttle at all it goes down to 22-24 hg.. Is that normal???

Somebody told me an exhaust leak could do something to boost... I'm 100% sure I have an exhaust leak where the downpipe connects to the rest of the exhaust...

If anybody can help me out by letting me know if this is normal or if it isn't what could be the problem... Thank you...

RE: B5 S4 Boost question...
 

id say vac leak... check all your vac hoses close to the N75 valve... at idle vac should read 19-22inhg depends on your alttitude.
is your CEL on? also check your stored DTCs...

My N75 went dead not too long ago and my boost pattern was weird going up and down and up and down... you can see the crappy video here
http://www.youtube.com/watch?v=GyRgUNO7PP4
i ditch the N75 and put in standlone MBC and fixed my problem.

RE: B5 S4 Boost question...
 

I to am seeing weard boost. I have heard the the N75 goes bad but how can i tell? and what is a MBC
I have a apr program and when i haid the car programd the guy sead that the stock paper fliter is just as good as a k&n? What is the best intake? And does a cat back exhuast realley help or shoud i just wate and save my money for down pipes

RE: B5 S4 Boost question...
 

I don't have a CEL on... How would the MBC work with a GIAC flash??? It wouldn't interfere with it???

RE: B5 S4 Boost question...
 

The only way to know if things are working fine is to do some logs on block 115.

Temp, humidity, altitude, & what gear you are in, will all affect boost. When it's really hot out, you will not see 17psi. It's a 17psi peak, not 17psi accross the board.
In 1st you are limited on boost.

18-22 is normal. But where did you tap for the gauge? Is this a cold or hot reading?

Going WOT on a cold car is JUST DUMB really dumb! The turbo's will not last long doing that.

So, fist thing
LOG block 115 & make sure your car is requesting the boost it's getting.
If that isn't in sync, check for a boost leak, then test the N75 as per the Bentley test.

I Have similar prob with my S4.......the guy who I bought this ECU said it is a unitronic stage 2 .....since its on my car I never touch the 20 psi...1st-2nd-3rd gear I reach between 12-15 psi max.......4th gear reach 15-16 psi...and 5th-6th gear I peek the 18 psi then drop to 16psi....and when I floor it in 4-5-6 gear I feel it like the car have not that much power.....

thats why im thinking 1st gear I was limited in boost due of the load....

but last week I talk with someone who have an S4 b5 stage 2 by unitronic and told me like 1-2-3-4 he hits 20 psi and hold it and for the 5-6 gear he peek to 20 psi then drop to 18psi....

so Im pretty sure my car have boost problem somewhere...need your helps guys!!!