Hi. I just installed a 4bar fpr to get more fuel overhead.
I have an audi tt narrowband amu.  K04 turbo.  stock injectors(386cc), high flow pump.
The original krtke was .083  so I did 75% of that and plugged it in. gave me .062
And it works.  kinda.

My problem is that it ran smooth at first (though with some light backfiring)
but after I did my first WOT pull the idle went very lumpy, and the car started backfiring all over the place.

On top of that, me7logger doesn't show anything for fuel trims. logging rkat_w, fra_w, fr_w don't show anything. It looks like the logger cant read them or something

Shouldn't 3/4 krkte be all that is needed? or is there something i'm missing when making fuel pressure changes?

3 to 4 bar is as simple as krkte x 1.17

I guess ill elaborate a little further. 386 x 1.17= 451. (386 x current krkte) / 451 = new krkte

Thanks Marty!   That worked.
Turns out I was running way lean.

I'm surprised that it was such a small decrease.
It went from .083 to .075. 
I would've expected a bigger change for such a big fuel pressure increase

A good start would be to do some reading about some basics in physics and a general book about engine tuning.
You are changing things without having any understanding how the underlying system works...

The flow increases as a square root from the pressure change.
So for going from 3 bar FPR to 4 bar FPR, it is sqrt(4/3.0)*krkte.
For inverse direction sqrt(3/4.0)*krkte.

This is very very basics physics. Of course if you do 75% of krkte it will be too lean. To get 25% you would have to increase the pressure from 3 to 4.7 bar.
And chances are that you don't know this either, but to produce a static pressure over the injector tip of 4.7 bar at 2 bar boost, the fuel pump has to be able to supply 6.7 bar.

Have you actually measured fuel pressure? From my experience (and measurement) old pumps struggle reaching 4bar pressure even on idle. Once you get in the boost zone you may only see a tad more than 3bar. Like 3,2bar.

Yes I am monitoring everything with a pressure gauge in cabin.  I'm seeing correct pressure at idle and proper increase as boost rises.   I have a kemso 265lph fuel pump.

I was going to try a 5bar fpr for even more overhead, but the kemso is rated at max 90psi.

I'm surprised fuel pumps are so weak max psi.  4bars come stock in many many 1.8t

ya that won't do what you think it does

if you mean fueling overhead, maybe, but after 4.5bar or more the fueling system starts getting very non-linear