I am wondering if the N75 in going bad or could one or all O2 sensers be going badbecuase some times the car makes its full 14 psi(APR 1 bar program) and some timesI get 12 or 13 psi even in 5th and 6th on the HWY.I have not dune a boost leak test beacuase some timesI get all my boost.The boost spike also changes some times 16 psi some times 14 psi.

 

Yes, that could be an issue if you havent changed it yet! Doesnt really handle boost that good at all... Just get a better aftermarket one and I think your problem will be solved!

 

Really? Do you mean aftermarket boost or stock settings? Where's a good source for an "aftermarket" N75...?

 

On the 2.7t, that is a false statement. No one makes a competent N75 for the 2.7. The H & R N75's will not work on the S4.

Boost will change with temp, humidity, & a variable of other things. A slight fluctuation is nothing to be worried about. If you think the N75 is going, there is a simple resistance test that needs to be done. It's in the Bentley.

If you want to test the car, run a vag-com log on block 115 & see what the actual boost is to requested boost.

 

I also have an APR stage 1 tune with a ECSN75 "race valve"and my boost fluctuates just as yours does. First thing in the morning on my way to work (after it reaches operating temps, of course), my boost spikes to about 17-18 and settles somewhere around 13-14 at higher RPMs. And while driving home in the North Carolina heat in rush hour traffic, I'll be lucky to get a 15 psi spike and a 12-13 taper. I'll even feel a difference in how much less it pulls at higher revs when it's hot. Cold, dense air just makes more boost.

 

Put in a normal N75 & you will get much smoother boost. The N75 R is fighting the MAP sensor & ECU, so it's cutting, & adding boost, giving you non linear power curve.

 

Geez sometimes I read the stuff that 2k S4 posts and think "wow, how does he know that ish?"....Impressive!

 

I was wondering if anybody has s bentley and want's to type up the N75 test... I really wanna figure out if mine is bad...

 

Thanks for the tip 2K!