Normal boost / vacuum levels

[cjep]

I have just swapped the TCV with one off my parts car, and I think the boost may have increased slightly. I will make a recording on my "test track" later to verify.

My next steps are (in no particular order):
- Replace bypass valve with high quality unit. My only problem here is I cant get one in Australia, and have to have it shipped from iPD in the US (=expensive) It is not fluttering, but it seems that some people get low boost from bad valves.
- Replace intercooler hoses with silicone hoses and nice strong clamps
- Continue to chase down vacuum leaks and replace vacuum hoses
- Replace TCV with a iPD heavy duty unit

I don't think all of these are needed to solve my low boost situation, but I do want to increase performance later on once I get things right.

[cjep]

So, just a quick update.

I installed a MBC so I didnt have to worry about the TCV leaking. Initially, I was getting about 13psi of boost, but after about 2 min or driving, this suddenly dropped down to about 5psi (max), i.e. worse than I had before I put the MBC in. I figured that the higher pressure made a hole somewhere ...

I have replaced all turbo hoses except for the little one at the turbo and made sure that they are all very tight. Zero difference.

Tomorrow I will replace the last turbo hose and the bypass valve.

PS: The cheap silicon hoses I got from ebay ($80 for the set) were a pig to put on, they were at times several cm longer/different than the OEM hoses! I guess you get what you pay for

[cjep]

Now I am back to square one. I have replaced the bypass valve membrane and spring, and the last turbo hose. I did get a small improvement in performance, but I am still getting only about 5psi.

As my boost levels dropped so suddenly, I figure a hose has popped off somewhere. I have replaced almost all vacuum hoses, and it is only the two hoses with white check valves that I havent replaced. One appears to go to the charcoal canister (and looks fine), and the other appears to go from the throttle body back to the intake side of the turbo.

Do these check valves ever cause problems? I guess the allow vacuum through but not boost?

What size leak would cause such a boost drop. Could it be a vacuum hose, or would it need to be something bigger?

Or could it be anything else? I think I have installed a new MBC, replaced hoses and CBV, and I was very careful to make sure I clamped down the hoses very well. I have looked at the intercooler and cannot see any problems with it, but it is hard to tell when it is sandwitched the way it is...

[eld4au6]

Have you checked for shaft play on the turbo? Could be going out.

[JRL]

6-7 in 1st is about right
An HPT should run at 10 at WOT, (2nd thru 4th gears) with maybe a small spike in 2nd, definitely in 3rd but WILL bleed off as the run goes on, that is normal
If the gauge is accurate you're just a hair down on boost, not much

[cjep]

My posts might be a little unclear, but since taking the video, I managed to get my boost levels up much higher with a MBC. But shortly thereafter, the boost levels dropped suddenly - as if a hose had come off. I have replaced all turbo hoses and almost all vacuum hoses, as well as the CBV, but without success.

I guess it is just a case of battling on, and replacing the rest of the vacuum lines...

[cjep]

I went through every vacuum hose. I found a bad check valve (the one closest to the manifold), but that didnt do much.

So then I went back through everything I had already changed, and my MBC was dodgy! I dont know if it had some grit in it, or if the spring is dodgy, but I have cleaned it out and started again and I am getting 10+ psi, albet with the spring much tighter than before.

Thanks everyone! I have learnt so much about this car by fixing these things, and now I have nice new silicone hoses everywhere

[abscate]

Can you report back your final measured boost levels and conditions so we can close the thread?