Hello everyone, all of the sudden my car is not boosting as it should, it used to hold steady 14/15 psi ( 1 bar ) and recently it will not go over 7psi expect in 4th gear where it goes to 10psi.
I haven't encountered anything like this before, so things i did was check for boost leaks and everything checks out, i also unplugged my MBC and it didn't change anything.
The actuator itself seems fine. I am just wondering if anyone had any encounters with something like this and what did you do to fix it... i am hoping i dont need to get a new turbo. Thanks!

 

- Faulty MBC or vac line to WG
- WG not closing all the way, sticking open
- Exhaust leak

Also visually inspect the turbo for fin damage or shaft play

 

With the hood up rev the engine a bit by the throttle body and check for any visual exhaust, or smell that would indicate an exhaust leak.

Take the air intake off the turbo as mentioned above and check it's health. WG is also a possibility.

 

If i plug the vac line from the WG, shouldnt it boost indefinately, or well as much as it can, since there's nothing opening the flapper? I am saying so since i did it and nothing changed with the vac line unplugged.

I would need to take the downpipe off to visually inspect the flapper, but it's definately on my things to do.

I've checked the manifold and the exhaust there are no cracks anywhere.


My valve cover is venting to atmosphere so it kinda always smells like exhaust around there, but i cannot visually see any cracks anywhere on the exhaust.

My turbo has no in and out play, and very minor side to side, but i guess thats fine for journal bearing.


What i really want to know is why is my boost in 1-3 gear 7psi and 4th gear 10psi, its really weird.

 

Need more info or pics of your setup. There are many different ways a WG can work, some have 2 vacuum/boost ports. Some are held shut only by the spring.

Its either your mbc spring/valve or your WG spring/valve not working properly.

Your 10psi in 4th is probably just boost creep from the faulty WG not opening all the way.

 

How did you test for boost leaks? Is your bov stuck partly open? Does your car sound any different, like the wg flapper is open under normal driving? Pull the down pipe and inspect the wg flapper. More boost in 4th is simply caused by more load on the engine.