Hi,

here an idea to control a water methanol injection by using the "intake air changeover function" on the original RS4 551K ECU.

The RS4 551K ECU has an implemented function to control the airbox flap.
I have blocked my open airbox flap, so I can use this function to control a pump for a water methanol injection.
To do this, I will disconnect the harness connector from the N335 and plug it into a relay to switch a electrical high-pressure water pump.
The N335 is connected to pin 44 of the 551K ECU.

There are 2 values and 1 map to control it:

KFLUKL [load/RPM] at hex 1A906 "Kennfeld zur Steuerung der Luftfilterklappe"
TLUKL [sec] at hex 1A946 "Verzögerungszeit für Schließen der Luftfilterklappe"

and

VLUKL [km/h] at hex 1A947 "vfzg - Schwelle für Öffnen der Luftfilterklappe"

With this info we can control a pump by KFLUKL over load and RPM with a vehicle speed threshold.

I will do this in the next month, because I don't have time at the moment.

The "intake air changeover function" is not documented in the ME7.1 Funtionsrahmen, because it is a special function only in the RS4.

Great idea,

because you don`t need a expensive additional WI-controller and can make a fine adjust water injection at high load with the given ECU.

No, it seems to be a digital 12 volt output signal from the ECU.

0V = air flap closed (over original N335 function)
0V => relais off => pump isn`t runing => water injection off (with new relais function)

12V = air flap open (over original N335 function)
12V => relais on => pump is runing => water injection on (with new relais function)

Is there a wire/connector for it in a stock S4 harness?

I have a 2000 S4 which uses an A-BOX ECU with an RS4 K file map, and it has a functional air-box vacuum control valve.  There isn't a wire in the harness, but one can add a additional wire to an ecu pin in the ECU harness.  I don't remember which pin number on the harness it was connected to.  I'm in So. Cal.  If you're interested in taking a look at the set-up, we can meet up if you like.

I am use k-box file too. Just flash k-box file. EEprom change is not necessary. But bear in mind that ideally the intake manifold and the throttle should be from the RS4 - k-box has a volumetric calibration for this inlet.

I like this thread. This is a really good idea. I will see if I can find the intake change over code in the 2001.5 Mbox ECU.

UPDATE:
I found this code in the 551K ECU, but it does not exist in the 551M ECU. If this code is in the 551M ECU then it is not using the same map format, which is unlikely. If you want to tune this map, you will need to run an RS4 based flash image. I don't want to speculate on how much work it would be to port this feature to the 551M ECU.

NVM means "never mind".

If it weren't for the German guys like you coming to the forum, there would be a lot less interesting stuff happening here.