NefMoto

Hey everyone! I need some collective wisdom here, been having all sorts of trouble with this particular car.

This is not the same car I posted here about. :)
This one is basically stock, but is also converted to MT.
The main issue is: it just won't control the boost correctly. It overshoots to the point of throttle cut, then tries to recover and so on.

I uploaded the bone stock binary just to see how it behaves at stock boost levels, and guess what - control is still out of whack. Log and ecuxplot attached.

2 main questions:
a) What can be at fault? We tried multiple different N75s to no extent, pressure tested, etc. Everything seems to behave normal, actuator arms move, etc. The only guess that remains now - that actuator arms are actually out of adjustment. Do the symptoms line up with that assumption?
b) How to deal with it? I mean - if it's indeed actuator arms, re-adjusting them with engine installed is almost impossible. So, can this be dealt with by re-calibrating PID? I mean, I obviously can lower the DIMX across the board to follow my requested boost level, increase Q2 etc. Or should I rather re-adjust KFLDRL? Or is it "proper" to re-calibrate whole PID like it's outlined in the according thread?

Where to dig, what to do with this beast? Some input would be awesome! Thanks!

EDIT: noticed that my ecuxplot screenshot has two purple lines - and I can't find the button to edit attachments. Anyways, the one at 100% is wdkba, and the one below is n75.
EDIT2: Modified the title to note that the problem is mostly resolved. Wastegate actuators out of sync.

Easiest solution would be to bring up req load to around 140-150 and see what happens.

Not an RS6 expert though, so take with a grain of salt.

Well, that's where I started.
It still overshoots like crazy, to the point of throttle cut. My ecuxplot is still misbehaving, but in the second (TC) graph, the car is actually modulating boost by the throttle plate while n75 stays ~constant. I can fetch logs if that'll help with diagnosis. Basically, the similarity between behavior with stock and increased LDRXN had led me to the belief that it's rather a hardware issue.

Note, in this case, the tune already has DIMX lowered and Q2 increased. Only ~10-15% for both though, not much. Just tried to see if there will be any effect - and these slight changes didn't seem to matter much. Next step would be setting KFLDRAPP to zeros and seeing how it runs on just the WG cans, I guess.

That boost drop/then upturn around 5000 is KFPRG/URL. They are a mess from the factory. Appear to be the result of day drinking. The rest, you need to spend some time and properly calibrate the boost PID.

Roger. Thanks!
Just thought it was quite weird to see that behavior with stock tune as well. But I'll just dig into PID then. :)

This. Not sure how common it is but it is somewhat odd, unless one of the wastegates are stuck closed.

Actuator arms seem to move in sync when control line is pressurized. But, what actually happens inside the turbo, obviously remains unseen. I guess I'll just do the CWMDAPP=8/KFLDRAPP=0 test, to see what's happening without the N75. I'll update the thread with results.

Actually now when you mention this, it all falls into place. You are 100% correct. I don't even have to test anything. It had always puzzled me - why did one MAF show higher readings than the second one. This is why. It had always stared me right in the face and I decided to ignore that fact. It wasn't that bad with tunes that requested a lot of boost (it was off by ~10-15%), but is extremely noticeable with the stock one. According to the graph, it appears to be WAY out of adjustment (Or maybe even stuck? But it appears to still respond to the control). Now I just need to figure which one it is.  ;D

Thanks and case closed.

Check this out:

Do your mafs match? Always replace in pairs. You can run the sensors out of any 2001+ wideband 1.8t as they are identical, just use the RS housings.

As for the boost, I didn't realize this was stock. Yes, something is not right. They don't behave this way stock.

No-no-no, MAFs themselves are perfectly fine. It just shows that one turbo behaves as expected and the other one spins out of control increasing the MAF readings on that side. :)
By the way, 955 cayenne turbo has the same MAFs as well, same housings and same MLHFM curve. The only difference is - cay ones have an aux temp sensor.

You say that, but if you swap them side to side are the readings identical?

Does the RS6 have independent wastegate lines?

One reference line from drivers side turbo, single N75 control T'ed to WGs.

So the wastegates should move identically to each other, and hence make exactly the same boost as each other?  (In theory!).

But, they're not?  Actuator adjustment?  Surely messing with software is only going to mess with the other turbo, rather than fixing the hardware issue?  Or did I miss something?

At this moment, I'm not 100% sure on what is the final cause. I have a strong feeling that this might be a heavily pinched boost control line to the "MAF2" turbo. Gonna re-test it.
"Fixing" it with software changes is out of question unfortunately, yeah.

Run with N75 electrically disconnected:

Never work around a HW failure with SW. Bad idea in general.

I also think it is a wastegate line issue.

Here's my RS6 boost log.

(http://i.imgur.com/fOXvLyu.png)

IDK how it will help though :P

Well, since this tread is now officially about bragging, I'll play!
Here's mine. Not a "boost log" per se, since I didn't have time to finish the 5120 yet, but a log nonetheless. :P

(http://i.imgur.com/8Je2MNw.png)


Anyways, jokes aside, on subject:
As suspected, the problem was with boost control. Not control lines, though. As it turns out, at some points in car's life, turbos were overhauled. And somehow noone bothered to correctly calibrate wastegate actuators preload. After re-adjusting them, this is what we got. There is still far from ideal, but at least curves look synchronized (see attachment, not the plot above).

I guess, we can declare this issue "resolved" and move on to the next one I'm having with this car in this thread (http://nefariousmotorsports.com/forum/index.php?topic=9566.0title=).
Thanks for all the input! ;)

Lmfao

Old post, but right one...

How in hell do you reach the passenger's side?  Can't even imagine.

Thanks!