AAZ loses power at 3KRPM (x-post from Samba)

[Syncroincity]

Guys, take a look at this post and see if anyone has an idea that can help him...

http://www.thesamba.com/vw/forum/viewtopic.php?t=567719

1.9AAZ based Syncro Weekender, Giles Super pump, VNT 17-22, water to air charge cooler, Donaldson air box, balanced injectors, big valve head, h-beam rods, crank girdle, ARP everything, all NEW less than 10000km ago.
  Happened all of a sudden a couple tanks of fuel ago, maybe 1000km ago, at 3000rmp on the dot, the boost gauge drops from about 14psi to zero, just like a charge cooler pipe comes off, but- if I let off the boost and power comes right back, and if I keep the RPM below 2900, you'd never know anything was wrong. Acts the same hot or cold.
  I've messed with my VNT controller, I even manually adjusted it while my son was driving- it acts exactly the same. I moved the pump timing from 1.05mm to 1.25mm back to ,90mm, acts the same. I replaced both fuel filters, acts the same. I even checked the .055' orifice in the return line banjo bolt, it's fine. EGT never exceeds 1000f even on the longest of pulls.
  I did remove my aneroid cover and diaphragm is fine, the fuel system is intact, letting air in the tank as fuel is displaced.
   Normally this van is a real power house... It's a good one, I'm used to solving these problems for other people, now it's my van that has ADD, like me. 
Any wisdom from one diesel vanagon guru to another?
Jeff

[carrizog60]

when it looses is power,does it smoke?

strange that boost gauge reads zero,on my vnt20 even i get off the go pedal at 3000rpm i will see boost...

[bbob203]

Sounds very similar to the problem I'm having with my mtdi.

[CRSMP5]

except his sounds like boost leak.. but im guessing internal vnt issue...

[745 turbogreasel]

Intake hose sucking shut.

[burn_your_money]

I would think a fuel restriction but 0 boost makes it kind of unlikely. 745's suggestion sounds good though.

[theman53]

Sounds like what my turbo did when the compressor wheel nut let loose. I still made boost, but maybe his shaft on the turbo or wheel or something like that internally is broken? Hose sucking shut is another good option, anything in the boost line system like that...intake manifold loose etc.

[carrizog60]

i assume that he doesn´t have any king of blow off valve in the intake manifold right?

[Syncroincity]

745 wins. 

Ok, I've got it! She's back. It was the least expected thing. The silicone elbow on the inlet side of the turbo. When the engine starts to haul air, it was collapsing and choking the inlet off, it still ran because it was feeding air through my crank vent tube at the inlet.
It was a good one, I couldn't have found it with out a second driver. It now pulls hard well beyond 5000rpm 21psi of boost. Now I need to set my base settings back.
  Thanks to everyone who ran to my aid...
Jeff