What would cause boost to drop dramatically?

[Mattheww044]

Hey guys, I was just curious what would be the causes of my boost significantly dropping in the higher RPMs.
I have checked all of my vac/ IC lines and hoses and snugged them all up with zip-ties or tightening the clamps. It seems to be dropping for 8-9ish psi down to about 5 in first gear.

While on the topic, I know that the higher the gear, the more boost you will see at WOT. But at this point, I am only hitting the 9ish in first and as much as 17-18psi in fifth on the freeway. Like I said, I know it is normal to see higher boost in higher gears, but is it supposed to be that dramatic?

Could these be signs of my vf-11 going out? Could I possibly be missing a leak somewhere?
Could a "faulty" BCS cause these issues? I am running an MBC, so my BCS is only hooked up electrically, so that is why I ruled that out, even though I have had the BCS CEL come on.

I am swapping my TD04 on as soon as I get my gaskets in the mail, hopefully doing the swap next weekend, but I would like to figure out what is causing this wierd boost issues one way or another.
Thanks in advance

[douglas vincent]

Try a "helper" spring on the wastegate. Sometimes the wastegate blows open when it should not... That was my issue....

[macipusy]

Are you running the stock BPV? I have blown up a few of those stock ones, and usually the symptom was no more then 9-10 psi in 1-2 gears and much higher in 4-5th.

Also be sure to check for any tears in hoses or popped off hoses off the intake manifold and around the MBC.

A good way to check for leaks is to cap off the intake at the turbo and blow air from an air compressor into the small line off the BPV into the intake manifold....blow air for a few seconds, then stop and listen for hissing.

[Mattheww044]

hmmmm... Douglas I suppose I will put the TD04 on and see if the problem continues. If it goes away than that would probably be the issue.

And Macipusy I am running the stock BPV, but i don't believe it is blown up. I have a spare I can try though. Hoses are all fine.

Could it possibly be my turbo going out? Or would those symptoms be more dramatic?

[Legacy777]

I don't think the turbo has much to do with this....other than what Doug talked about for the wastegate solenoid.

You should not see that large of a boost swing. Honestly, I would suggest going back to the stock boost control and see if the problem still exists.

I'd tend to agree with Maciek's analysis. Pull the BPV and try blowing throw it to see if it leaks.

[Kelly]

BPV was my first thought too.

[Mattheww044]

ok, I will try swapping the BPV, and if that doesn't work then I will try going back to the stock BCS as well. If the BCS does solve the issue, then that would indicate that the MBC/lines are leaking I take it?

[Mattheww044]

Ok, my Bpv is definately leaking. I would have checked that, but I just put on a metal one from a supra. When i put it on there was no leak at all, but after checking it no, there is literally no resistance, its like blowing through a straw, both ways. Thanks again