I just installed an AWE K04 kit on my nDBW A4 and the ECU is cutting boost down to 5psi at ~5500rpm. I've been trying to figure it out on my own for a week now, but I'm a bit stuck. Here are the symptoms/data I've been able to gather....

-- holds 19psi peak boost
-- pre-cat O2 reads .76-.84 @ WOT
-- long-term fuel trim: ~0% at idle, -11% at part-throttle
-- MAF reads up to 187g/s
-- not detonating: knock sensor voltages ok
-- no misfires
-- no CEL/DTCs

If I unplug my ECU and reset it, I can make a few runs up to ~6200rpm w/o boost being cut. The MAF will max out btw 5000-6200rpm. After that, it will start to cut boost at 5500rpm and the MAF will only read in the low 170s from 5000-5500rpm.

I suspect a boost/vacuum leak since I can hear the BPV (710N) during shifts, but I cannot find a leak or disconnected hose anywhere. Should the pre-cat O2 be changed? I have 83k miles on it. What would cause my O2 to read lean and fuel trim to read rich? Anything else I should look for?

A couple of block 31 graphs at WOT:
<img src="http://awot.dofu.org/audi/o2_1.gif">
<img src="http://awot.dofu.org/audi/o2_2.gif">

It looks like you go way lean at t=11.5 in the second plot.

why would the O2 sensor lean out when LTFT is running rich?

<img src="http://awot.dofu.org/audi/o2_3.gif">

stays around .8
<img src="http://awot.dofu.org/audi/o2_4.gif">

Log injector pulse, I forget the block. The trim is trying to make it richer, but the injectors may be maxed.

causing the ECU to add more fuel thinking it's lean which ends up making it too rich?

since it is no longer used to help set fuel. The only thing that is doing that is the maf and your already running max with that.

Hitting .7's is a bit lean and not really where you want to be. Want to stay close to .85 if possible.

or lifted off the throttle.

Put it on a 1552 and dont guess, it costs lots of money to guess;-)
Rod

How long does it take you to get to 19psi? Where do you have the boost gauge Tee'd into? Try another boost gauge too.

Log your throttle angle, if it is not closing, which I dont know how it would... you must really have a big leak, or your wastegate is opening. A matter of fact it almost seems like a wastegate issue.
You know what psi spring is in the wastegate? You running a boost controller or N75 valve? If your wastegate sspring is 5psi maybe for some reason your wastegate is opening?

Cause with a boost leak that big I bet it may trake a little longer then normal to get to 19psi and I thibnk you would realize this.

So obviously you can feel a power difference when the boost goes from 19 psi to 5?

I hit 17psi at around 2700-2800rpm and 19psi at around 4000rpm. I have the gauge spliced into the vac line at the front of the intake manifold leading to the bpv. I've had this gauge before the K04 so I don't think it's a problem.

My throttle angle looks fine except it only opens up to 78° max and I've seen logs by others where it opens up to 85°. I don't recall if it's closing or not. I'll have to check my laptop and see.

The wastegate is set to whatever AWE sets them to, so I have no idea what it is. I'm running the stock N75.

Yes, the power loss at 5500rpm is very noticable. It runs strong then all of a sudden boost drops to 5psi. Sometimes it holds up to 6000 to 6200, but power always drops after that. These past few days I've been reluctant to take it past 5k much due to what usually happens after.

Gas mileage is also down 3mpg, but that's probably mostly due to the 5bar fpr.

That issue only happens with dbw's since the ecu can control the throttle body when it wants for safety issues.

my friends S4 used to behave the same way, would run fine after being reset and then go into limp mode, a new MAF fixed it for him, but it sounds like your MAF readings are good. could try swapping a new one in just to see.

I think I'm going to try a new MAF and new O2 sensor and see how it goes.

I would spike to 25 then hold steady at 5 psi(limp mode)did every logical test we could think of only to find that a tuner that I had gone to before K04`s were installed put a darn Race n75 valve causing boost spikes.I replasced it with stock valve and I have no more problems.

to bypass the N75 valve and see if it boosts faster without the delay.

Seems like
Huge boost leak
N75 or boost control issue
Wastegate issue.

G-Luck, sorry in hurry :-)