Fluctuating overboost?

[PlanZero]

OK, I've spent the last hour searching and I can't find the definite answer, so bear with me. On my 96 Tsi fwd my boost gauge fluctuates rapidly between 10-15 at WOT. I just installed this gauge, and I was going to install a NXS MBC but I want to figure this out first. The car pulls perfectly, but I can almost hear the fluctuations when this happens. I also installed the same gauge on my 97 Tsi with no problems. I was thinking boost creep due to my 3" exhaust with unported o2 housing, but that doesn't explain the fluctuations. She boosts fine, then the gauge starts to bob back and forth from 10-15 and no more. I'm pretty sure it's not spiking either, since it doesn't really settle.

Car is mostly stock.
T28
Injen intake
EBay 3" exhaust (no cat)
Sunpro boost gauge.

 

[2gmitsueclipse]

you should not be boosting to 15psi on the stock boost controller. It may be possible to spike at 15psi with the restrictor removed. You are close to needing some fuel upgrades (rewire, pump, injectors, logging/tuning software). Here are a couple of things to check:

• Boost leak test. I am tired of posting the how to's, so check my previous posts. (Youtube videos)

• Check the operation of the wastegate actuator. Check that it is operating properly. You may need to take off the o2 housing to inspect the flapper as well.

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• Check for exhaust leaks by the exhaust manifold, turbo-to-exhaust manifold, and turbine-to-o2 housing. black carbon deposits are a sure sign of a leak. There may only be leaks at higher pressures.

 

[PlanZero]

OK I forgot to mention I removed the little plug from the bcs awhile ago. I did a BLT on both cars last week. No leaks. I also just installed hard smic piping and a greddy type s before that. I'm missing one exhaust manifold stud, but when I ran seafoam I saw no smoke from anywhere around the gaskets or manifold. I wasn't planning on pulling the o2 housing until I got some further information. Is there an easier way to check the wg?
I still don't understand why it's just bouncing between 10-15 psi. If there was a leak wouldn't it fluctuate lower, and not go so high? Is this dangerous? Is it possibly gauge related? Otherwise it seems to work fine. Would installing the MBC improve or worsen my condition, or should I just wait? Thanks

 

[inthemidst]

Check the wastegate hoses for kinks or holes check your blow off valve to see if it holds pressure

 

[2gmitsueclipse]

I have edited my first post with a video to test the wastegate.

 

[2gmitsueclipse]

Check the wastegate hoses for kinks or holes check your blow off valve to see if it holds pressure

If the OP boost leak tested his system properly, a leaking bypass valve would have showed up. It should be set at about 20psi for his setup. If the bypass valve was the stock plastic one, it would for sure be leaking.

 

[PlanZero]

That didn't sound like diddy
OK I checked the wg. Seems to open and shut properly. I also did another BLT and found a small leak at one of the hard pipe couplers. Must've loosened a bit after install. I haven't had a chance to take her for a spirited drive yet, so I don't know if that little leak was it. I was going to install this NXS MBC in the morning. Is this advisable?