NefMoto

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?

No that is extremely completely wrong lol, use KRKTE calculator instead.

3 to 4 bar is as simple as krkte x 1.17

Isnt that making it even more rich?

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

or just subtract 17% from your current krkte. Whatever floats your boat.

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

Update:. So I was curious why the krtke change was so small.  And decided to try stock 3bar krtke with the 4bar fpr

It works just fine! Car runs smooth.

So. What gives? Why can I simply up my fuel pressure without needing any changes?

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.

.083 to .075 is the same change as 83,000,000 to 75,000,000

would you consider the latter to be a "small decrease"?

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.

Ooooh.  That makes it more clear

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

Uh thats not how it works? "overhead? What do you mean?

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

Yes.  I'm just trying to stretch the capability of my 386cc injectors.
They max out at 270bhp.   I'd like to make 300.

Yes.  I'm just trying to stretch the capability of my 386cc injectors.
They max out at 270bhp.   I'd like to make 300.

figuring out krkte is more effort than an injector swap, may as well do both if you're gona do one. old standard injectors fail, sometimes slowly and that will obvs cause more issues

Just get 550's or 630's.

I paid like 160 for OEM Bosch 550's and a few euro's for the adaptors.

My car has those long neck injectors. Heard of any cheap ones of those?

Also I will be big turbo eventually so I'd want at least 750cc or maybe just go 1000cc and forget about it

Good point. I tested and cleaned mine but they have 210k miles on em.  Maybe their max potential is weakened?