I am a beginner in tuning. I’m in the process of tuning a 2.7t that I’ve stuffed in a Boxster. I’ve got fueling right about where it needs to be using a different MAF setup and intake arrangement. I’ve gotten this nearly dialed while operating under the 5k rev limit due to lack of vss to ecu.

I’ve recently created a vss translator that feeds a nice signal to my ME7.1 ecu (t-box flashed to m-box). The signal works and is read as verified by logging vehicle speed from the ecu (selected gear calculation is also functioning correctly).

My question is around what maps the vss influences in the tune. I know for sure that a few things happen when the vss is hooked up:

1. The 5k rev limit goes away (this is good and expected)
2. The revs hang, even surge a little, when shifting (not much, maybe 500ms-1sec, but enough to be super annoying). When I drive it with vss disconnected, the revs drop instantly and make for great fast shifts.
3. The fueling changes in that my A/F goes up .5-1 pt. Again, when I drive with the vss disconnected the A/F is back where I intend it to be.

I’ve searched and haven’t found anything regarding these behaviors… apologies ahead of time if I’ve overlooked the answer… can someone point me in the right direction?

Yes, gear detection uses vss as a part of its calculation and have verified that the correct gear is being calculated.

Are you aware of anything else that uses vss? Or is gear detected used in a map that would contribute to rev hang or fueling?

Thanks!

Hmm good question, I’ll check this tonight. Thx. Doesn’t explain A/F but could be 2 different things going on.

I dont no if still actual for you, but if you want to check:
1. I had same problem on 1,8T, where is more rpm limiters, look at my post how i solved problem and running without vss signal. http://nefariousmotorsports.com/forum/index.php?topic=17021.msg154007#msg154007

Good call, I’ll check the brake signal too. Thx. I’ll have to learn more about anti judder. Right now the drivability is really great with vss NOT connected (aside from the 5k rev limit)… with the vss connected I get rev hang (root cause likely = no clutch signal to ecu) and it appears fueling is affected (though I now feel like I should do some more logging to verify).

Again I need vss working to drive gear detection because I ultimately want to implement gear dependent load cap.

As an aside, I got vss working using an Arduino which monitors the passenger rear wheel speed sensor (which outputs a .8-1.8v ish signal) which uses a mosfet that pulses ground to the audi ecu.

Thanks all.

left foot braking, possibly other things as well. you'll have to search the FR

Thanks prj, this helps me know where to look. I appreciate it.