NefMoto

I've got an interesting one for you. ;D
RS6, SRM hybrids, 5120'ed binary.

Problem: sometimes at some point in the pull one MAF falls flat on its face, the second usually follows shortly after. Boost can drop below wastegate spring pressure. What can cause this? I've captured a weird one - where small variation in N75 duty causes one MAF to demonstrate pretty much "on/off" behavior. Throttle stays 100% open, N75 duty seems to be relatively stable when this first happens. It can get upset afterwards, but never seem to be the initial cause.  This seems relatively random, but tends to happen more as boost is increased. Log and a couple of plots attached. Any ideas?

EDIT: it appears that the issue was two-fold. Leaky diverters - replaced those with Forge units, and WG preload was off on driver's side turbo. I'll update this post once more once we confirm that the issue is solved (hopefully).

gigantic boost leak?

Got wideband? If not, you should have one anyway.

Actually, I take that back.

MAF is dropping with ps_w following actual boost.

I think your wastegates are failing and are not holding as flow goes up.

As an experiment, try allowing your I-limit to ramp back up to 100 after 4500 to 5000 rpm or so.

That's actually what I had in mind about wastegates. Just didn't speak it out loud to hear other possible options. :)
But well, this seems like the only possible case when boost drops below spring pressure (edit: and ps_w follows).

I'm a bit hesitant to let those turbos go "all out" even at top end, but might be worth a try for testing purposes.
I don't like how these hybrids are built - they have a gigantic cold side, but pretty much a stock hotside (which is already severely flow restricted in stock form).

accordion hose collapsing?

Good call. This is definitely a possibility.

There is an accordion hose on a c5 rs6?

slow guy is right.

Could it be related to DVs allowing air to recirculate back into turbo intakes?
We've replaced them with new 034 ones, but this has never fixed the problem.

No, because ps_w is following boost.

I'd look towards wg issues first, then some sort of blockage (intake, exhaust).

Dug up some logs from the car with confirmed bad DVs (or actually improperly plumbed). Here you go. ps_w follows as well.

I dont know I still kinda think DVs, but I'm used to being wrong. We have been though alot
on the car and no other problems, and I have seen these turbos on a rs6 perform well.
Thus I'm kinda doubting the WG problem, but this car has Cats and the other rs6 did not.