Horrible Boost Problem

[TurboAWDKID]

ok, so i have searched the entire web for this and cant find an answer. i have replaced my bov gasket, jpipe gasket, tb and tb gaskets, all vac/boost lines, couplers and clamps, wastegate, and checked torque on spark plugs as well as all connections and clamps numerous times. when i pressurize the system (at the tb), i can build boost up to whatever i want, but it falls off rapidly until about 10psi when it stats to slow down. when i pressurize it at the turbo inlet, the same thing happens. i have also pressurized the system backwards starting just before the tb elbow towards the turbo (with the compressor inlet blocked off). i have fixed every leak i can find and i cannot find any more. yes i used soapy water and i cant find any more bubbles, nor do i hear any leaking. all of this was done with #1 piston at TDC also. my boost controller works just fine, as it bleeds off air at different pressures depending on how i set it (SBR MBC). my car idles fine, so it doesnt seem to be a vac leak. randomly while driving i can hit full boost (15psi) but it falls off to 6psi around 4k. most of the time it just builds until i hit 6psi and never increases. any thoughts?

 

[DSMunknown]

Sounds a little bit like the PCV valve staying open under boost.

 

[TurboAWDKID]

unless its getting stuck open when a vac is put on it, it works fine. i already took it off and checked it. i could only blow through the side that screws into the vc. monday im taking off the front mount core and testing that seperatly. this sux. i can only hold 6psi, sometimes 10 and i have the mbc set to 18psi!!!

 

[danameisoj125]

i experienced the same problem and it was my boost controller. i would spike but it wouldnt hold and do the exact same things your saying . i changed out the bc to a turboxs and the problem went away. see if you can borrow a buddies bc and see if it does anything different.

 

[TurboAWDKID]

i thought i ruled that out since i ran the car w/ no bc and no w/g and it still wouldnt boost properly. but i guess anything is worth trying

 

[oldman]

1. TDC is the worst place to be during a boost leak test.

2. Boost leak is only one of many possible causes for your condition, exhaust leaks, wastegate and turbo itself are the other possibilities.

3. Please use proper punctuation and caps when posting in the tech sections.

 

[TurboAWDKID]

Well the only exhaust leak I have is after the turbine housing. It is at the o2 housing to downpipe. My turbo has no shaft play and it is only 1 year old. It could be the wastegate I guess, but this wastegate was never a problem before.