Hi, I've been lurking on this forum for quite some time.
It has helped me tremendously with ECU tuning basics and I would like to thank everybody that contributes here.

I have a background in tuning diesels and old school carbureted petrol engines so I thought I could try to tinker with my daily driver a bit

Engine is 2.0 TSI 200 hp CCZA and it is completely stock

I have succesfully tackled "stage 1 tune" which resulted in 260hp 420Nm on 100 octane petrol.
Now I thought I could try to tune it on E85 and I have encoutered a broblem which I'm unable to solve by myself.

I dialled in KRKATE so that idle and partial trims are all within 1.5% and car runs great except for for WOT at 4500rpm onwards.
From idle to 4500 rpm everything is fine - requested lambda follows actual as well as rail pressure and engine pulls very strong.

But at 4500 rpm something weird starts to happen.

Rail pressure follows request as it is supposed to,but injector opening time suddenly goes up and actual lambda starts to lean out to an extent that I get a nasty torque intervention - boost cut and sometimes throttle cut.
Does anyone have any idea how is this possible?
How can mixture get leaner when fuel pressure is OK and injector stays open for longer?
I will be grateful for any suggestion

Log, original and tuned file attached.

You need 30% more injected fuel mass for E85, when you squeeze it even more.

Consider that in your thoughts, just a fast switch to that fuel will not work well mostly. Many hours reading needed, sometimes one ore two new cylinder heads

I did not opened your file, i speak in general.

You forgot about eficency. Lambda and Ignition eficency. You can make rough estimations like that but no layout of systems.


If you squeeze the system to get 360 HP on pump gas, eficency is bad. You will probably need 1,4 times of fuel to get stable combustion without too high peak pressure. Watch lamiar flame front velocity  charts over lambda for alcohol fuels for that.

Maybe someone on sea level on a nice cold day managed to get 360 HP out of the pump, but how sure it is that ot is always possible under all conditions?


So calculate maybe 340 Hp as maximum with 100% pump gas duty cycle. Substract 40 percent and you are already below your current power output.



Remember: i speak in general, have no experience with that engine or specific ecu.

Yes, if you lower the FPR pressure.

I have not bin able to look on your file, but I'm doing 320-330whp with K04 turbo on stock fueling parts and 98 pump fuel.
So you should be able to run E85 with stock turbo. As I say before you need to look on LPFP and HPFP tuning.

Could you be more specific, please?
What maps did you alter in your file that enabled you to safely run 330whp which is surely over 360hp at the crank.

I'm very new to tuning MED ECUs so only thing I was able to do was alter KRKATE and slightly increase rail pressure in part load.
I was unable to increase pressure at full load, although I modified all seven fuel rail maps and everything that even resembled a limiter, but rail pressure stayed at stock value of 150 bar no matter what I did.

I also tried decreasing rail pressure but problem remained the same only thing different was longer injector opening time, but lambda leaned out exactly the same.

So, I've had couple of sleepless nights over this, but I can now proudly say that I solved the issue

Problem indeed was in HPFP and LPFP calibration.
Firstly I increased LPFP duty cycle but that has helped only slightly. (Note: in VCDS - Advanced measuring values there is a "group" with Rail press spec., Rail press actual and fuel pump duty cycle. Spec and actual are values for high pressure fuel but said duty cycle is low pressure pump duty cycle. Maybe this is common knowledge but it sure had confused me at first.)

Then I tried to increase Rail pressure but it never went over stock 150 Bar no matter what was specified in the map. I increased every limiter I could find but none of it had any effect.
Then I found out that "main" temperature dependent fuel pressure limiter was somehow screwed up in the damos so I altered it directly in hex code and now I finally had 170 Bar of rail pressure which fixed my fuel delivery Issue.

Now, (apart from slight dip in rail pressure around 3000 rpm) I have stable fuel delivery throughout the rev range with reasonable injector timing so it seems that it really is possible to support equivalent of 350 hp on stock hardware

Sounds painful!