To4b can't boosst past 15psi

[krummel21]

I've read a couple forums where people had similar problem, I just wanted to check to see what might be the problem and what I needed to do to fix it.

 

[oldman]

1. Check for exhaust leaks before O2 housing.

2. Make sure the flapper is fully closed, adjust if needed.

3. Perform an "all out boost" test run by leaving the actuator nipple open, expect all out boost so feather the throttle accordingly. If you're able to to boost past 15psi, the actuator is opening prematurely or the mbc is defective. If problem persists, go to 4.

4. Test run with the flapper wired shut, again expect all out boost. If problem solved, the 38mm flapper is being blown open by exhaust flow (seems to be a common problem with to4b), try pre-loading the actuator (shortening the arm by a lot then force it back on the lever). If problem persists, go to 5.

5. Perform a complete boost leak test and make sure you're able to test up to 20psi. If the problem still persists after the leak test, you can say with almost 100% certainty that it's the turbo.