NefMoto

Hi

I've this issue with a car that has a sudden boost loss and some
fluttering in MAF voltage a bit higher up the rev range.
This only happens in 4 and up gears. It's a 2.7T with k04 hybrids.
I have no idea what's causing this so I am putting it up here maybe
someone will have a glory idea.

Thanks ;)

Flutter >5k looks like surge to me, not sure on the boost drop earlier though

I noticed in that log that the flutter starts at camshaft changeover.

I did another log today, it's really bad, and I can't find any hardware fault.
I'd really appreciate a glory idea ;D

And as a reference here is a 3rd gear pull as well which does not show
this symptom.

Just lay off the boost a couple of psi in the problem area...

Apart from that, bigger/laggier turbo (or large turbine housing) so you don't hit the surge point :)

Well the turbos have no problem making that boost in 2nd and 3rd gear around 4k, so I don't
see why they can't do it in 4+ gears. For the fluttering, sure i will decrease boost but the low
rpm range sudden 0.5 bar boost loss is what bothers me really.

You make boost earlier in the higher gears with more load, thus you're making just a little too much too early.

Think of it as an issue with the turbos being too efficient at low rpm. The engine simply can't consume the airflow (for a multitude of reasons).

Could have a dabble with the gear based boost and slightly lower it in the affected rpm's in the higher gears?

Just some ideas...

I understand what you are saying, I just never did saw such low rpm surging, and to be honest
I don't know how it looks like on the logs, and I can't hear anything weird in the car either.
It's weird though the engine has all the bells and whistles with ported heads and all and the turbos
are not that big, anyway I did what you suggested and attached a log, now i guess i need some more
duty cycle up top to bring boost back up. Thanks

When I came across surge I found it would cause the boost drop when it occurred heavily, but just slight chuffing (sometimes not audible on the road) can be read with those wobbles on the maf.

If you're right on the edge of surge, maybe the weather has made it worse/noticeable now?

Good luck :)

I think it's fairly obvious now...  :-[

https://www.youtube.com/watch?v=Hl2f808QvEk (https://www.youtube.com/watch?v=Hl2f808QvEk)

I am really disappointed in all this now. It would be nice
to figure out what's the restriction at this point. Time for bigger cams?

(http://i.imgur.com/P3IWeLE.png)

(http://i.imgur.com/qJrX05a.png)

Measured exhaust back pressure today before the turbo in the exhaust manifold,
and it peaks at 2.5bar and stays there while the boost pressure is at 1.6 bar and
it still surges at 1.6 bar, which is nothing.  :-\

Disable vvt?

Odd that it is happening near the crossover point.

Yes I did that today already, no change at all. Moving the switchover point
to 6k did not change a thing either.

Hmm. In one of your logs, your battery voltage seems super low... 13.3 v... maybe alternator/battery/electrical?

Bad things seems to coincide with crossing 13.5 volts

I actually have a brand new alternator, i was only getting 12.7 v -ish charge previously.
I think 13.5V is acceptable with all the electrical stuff on and two walbro 450lph e85 pumps
going. I don't see how voltage could relate to this.

How old is the battery? Can't hurt to try a new one. It isn't as if you have any other clues right now... 13.3 is pretty low

1.5 years old maybe. but sure i can try a new one, it only costs $150, will try tomorrow ;)

Wish I had better advice for you :(

Could you check some other car's logs in case you have them handy?
I wonder about the voltage there.

im generally seeing 13.7 ish at the lowest

But very few of my logs have ub, so I don't have a good representation.

My battery voltage drops between 12v and 13v at full boost. No issues here.

So I went crazy today and did two things.

#1 run the car without intercoolers, quickly bypassed them (no pictures sorry, i forgot to take 'em)

I saw a sudden overshoot of boost on ramp up, so I had to fix wgdc to 50% to see what's up and I noticed
that there is basically no surge at all at 1.6bar of boost, I stopped at 6k rpm because I knew IATs will be super high, well for sure
they were. 100C at 5.5k RPM and ECU pulling timing down to 2 degrees... thank you E85. ;)

Then I figured I have to try something else. I remembered from Flyboy's testing that the OEM RS4 intercoolers
flow better than the ERs, well the only problem is that I only have one handy, the driver side.
... but hey I have a set of C5 RS6 intercoolers which are GIGANTISCH (ref.: https://www.youtube.com/watch?v=5WSkKUjizxU (https://www.youtube.com/watch?v=5WSkKUjizxU)).
Since I did not have enough silicone couplers for doing both sides with the RS6 coolers,
I did the driver side with the RS4 and the passenger side with the RS6 cooler.
I think I could not fit both RS6 anyway, they are really huge.... I mean it.
Don't laugh at me, this is eastern european style.

http://i.imgur.com/qSdP061.jpg

http://i.imgur.com/NtB2lkc.jpg

I also did a reference run with the ER coolers an hour before I installed these here are the results.
First is the ER then the RS6-RS4 combo.

What do you guys think?

And here are the files.