Boost Problems!!

[TSi95AWD]

My problem continues with not being able to hold boost.

I am tuned and set at 20 psi. However, it will not hold.

1st gear - holds
2nd gear - spikes 21, falls to 20
3rd gear - hits 20, gradually falls to 18
4th gear - hits 20, falls to 16
5th gear - only goes up to 15psi!!!!

I thought originally it had to be a boost leak. But after an intake pressure test not finding a leak, it still does it.

There are a ton of things i figured it could be. But im not sure about any one of them.

Im getting a custom o2 housing built soon, but im not sure this is going to help the issue.

Any suggestions??

I have a PTE T3/T4 GT3251 internally gated.

 

[greeneclipse]

what kinda boost controller are you using????

 

[TSi95AWD]

Dejon Tool MBC

 

[greeneclipse]

maybe your wastegate flapper is blowing open under high boost

 

[1fast97gsx]

I have a similar problem with my tial 38 wastegate. I go my new injectors installed so I wanted to raise the boost to 24ish and 20 is the highest it will go and then it just sits there. Not sure what's going on.

 

[Lurker]

What's your boost level without the MBC ?
An MBC delays the opening of the wastegate by not letting the wastegate sees pressure until a preset boost value has been reached.

If your wastegate does not have enough preload, it will still open even though the MBC is delaying the signal.
It will be blown open by your exhaust flow, as mentioned by greeneclipse.

So, make sure you have enough preload on the wastegate by checking your boost setting with the MBC bypassed. You should set the preload to the minimum amount of boost you ever wants to run.

When I first installed my GT3251, I had too little preload on my wastegate ( without an MBC), and it was causing a very laggy spoolup.