Hey everyone, I was the guy with the orange 850 turbo way back when and a little over a year ago I bought another 850 turbo to rekindle that lost love. The orange one has been gone a while.

Here is my deal, I have had a 5 psi drop in boost from expected numbers. When I had the stock ECU in, I was boosting around 5 when I should have been hitting 10. Now I bought an IPD ECU on facebook recently and now I'm boosting 10 psi when I should be boosting 15.

Very first thing I did was pull the wastegate line to make sure my turbo was capable of making more boost. Sure enough, I boost around 13 psi no problem. Ruled that out. Then replaced my OEM TCV with the Delco unit others are using. Did the relearn procedure and when I did that, it would boost up to like 12.5 psi and flutter for the first few times as it was still learning. As it began to learn, it started regulating boost steadily at 10 psi (with IPD tune) and now it's locked there again. I figure the OEM TCV was probably fine. Still using the Delco unit tho.

So far, i found that IPDs stupid block off plate for the CBV was leaking. When I did research, I found that most peoples leak because the gasket is lame. I used gasket maker on the block off plate and now zero leak there.

Then I performed a pressure test by connecting a small capacity air compressor (for filling car tires) to the boost tree via a silicon line and secured a pipe end to the hose clamp at the turbo. So turbo is not part of the test and I am testing from just after the turbo all the way to the intake manifold. I plugged the small line that is part of the PCV system that runs from the manifold to the intake pipe so that I could hold better pressure. I hold pretty good pressure but I notice that when fully pressurized, the EGR valve diaphragm sounds to be leaking, I can feel it too. It is a very small leak but it sounds like intake air can slip past the valve stem which I am sure is not a big deal because of just how small the leak is.

Question is, with no considerable boost leaks, and two TCVs behaving the same way, what could be causing the lack of boost? It's just so confusing because the car drives great and behaves like it is supposed to be regulated at 10 psi when it should be regulated at 15. What I means is it spool to 10 just like normal and holds incredibly steady. Also, what is the purpose of the PCV line that runs from the intake manifold to the intake pipe? It's like a designed boost leak and during my intake test with the small compressor, I could hold no pressure unless that was plugged.

Sorry for being long-winded. TIA for any help.

 

Here's a video of just how steady it holds. And yes, that's a BOV in the video and no, it does not leak. IPD mentioned that should be first suspect.

 

Hmmm, what year is the car? I don't think the turbo cars are suppose to have a tube from the tree to the intake tube.

A hole as big as one of the tree ports can leak out 5 psi.

 

Car is a 95 turbo. It does not lead from the tree to the intake pipe. It is on the passenger side of the intake manifold (nipple) and leads to the intake pipe. It's actually a part of the PCV system.

But when the car is under boost, air is just allowed to freely bypass through this 1/4" line back to the intake pipe just like a leak. The car doesn't idle rough because this metered air is not leaving the system, just bypassing from high pressure to low pressure. On the 850 since there is no electric heated PTC unit, I think this is supposed to keep the PCV line to the intake pipe from freezing because the turbocharged air is warm. But it causes a leak in my opinion. I don't get it.

The S60R has this part of the PCV system on the intake manifold as well but I believe it has a check valve built in so when under full boost, there is no flow. I think the idea is, while cruising, the intake manifold has greater vacuum to help excavate combustion gases ; during boosting, the intake pipe has the greater vacuum and the check valve is closed so you don't bleed turbo pressure.

 

Oh, I get it, mine is '95 as well. What other mods do you have? A common issue for turbo's that restricts boost is exhaust. Need a large down pipe to get the hot air away from it and let it spool up to higher speeds.

 

I would tend to agree, but that wouldn't make sense why it's been a 5 psi drop with stock tune and then with IPD tune. Even with stock downpipe, I should be able to hit stock boost in full.

Having the PCV line which connects from the intake manifold to the intake pipe (preturbo) is no different than having an open nipple on the boost tree. I might just plug this line and see if I get the 5 psi I have been searching for. But it still wouldn't be right because that is the stock design.