Just recently I've been noticing that my boost has been coming on way too late. Normally I'm supposed to reach full boost (10psi) at 2900rpms -

The other day I noticed how late my car took to reach full boost. In fourth gear I floored it - at 3200rpms I only made 6psi, it took till 4200+rpms to make full boost ~ 10psi.

The next day I started in 2nd gear around 1000rpms and floored it. Typically I start to see boost at 2000rpms -- yet it took till 3500rpms to see boost, I redlined and still never made full boost.

I don't have any exhaust leaks from engine to manifold - or from manifold to turbo(or any leaks period). I have a full 3" exhaust, no muffler, magnaflow cat.

My only guess is that my wastegate spring has worn out, and is opening too easily now. If you all remember, with the 745i setup, my max boost w/ an unmodified wastegate is 10psi because the valve tension force can be overcome by the pressure in the manifold.... forcing the wastegate open. Maybe it's opening too easily with a worn out spring.
Either that or the seal around the valve is worn or missing, allowing exhaust gasses to work around the valve.

Any ideas guys?

Couldn't you test your wastegate by playing with your boost controller? Is it possible the wastegate is just not receiving the signal? Maybe you melted a boost line or something. Also, how do you know you have no leaks (pre throttle body).

Do you hear ANY unusual noises now that you didn't before? (Air leak type noises?)

What are you using for a bypass/blowoff valve?

Boris

Well -- First off I'm using the 745i setup, non-intercooled.
My intake setup is pretty easy -- Turbo -> piping -> Throttlebody, there's almost nowhere to leak boost in the pipes that I couldn't have already found.
The boost controller serves very little purpose, my boost can only be adjusted between 6 and 10psi. 6psi is when the wastegate opens when it sees full boost. 10psi is the most boost I can make, even if I completely disconnect the line to the turbo.
And usually when I have a vacuum//boost leak - I will hear a very strong whistling noise. No such noise. Yet even when I heard the noise, it never affected my spooling times this dramatically.
And the BPV is a cylinder type valve, the cylinder is perpendicular to the piping -- and is lifted up around 15-20 vacuum, otherwise it's weight drops it down and keeps it down.

So what type of bypass valve is it? Who makes it? It could make a difference if it's a Bosch type with a diaphragm.

So let me get this straight, you can disconnect your wastegate completely? What happens when you do that? Which wastegate do you have? It's possible the wastegate is kaput? Is it the original 745 w/g?

Boris

There is no brand name on this stuff - It's OEM BMW. The BPV is part of the 745i chage pipe, no names or anything stamped on it. The design is very simple:
Metal cylinder sitting inside of the housing next to the charge pipe. With enough vacuum the cylinder is pulled upwards (against a spring) and allows boost pressure to escape out of the charge pipe and back infront of the turbo. No amount of boost pressing on the cylinder will make it move. Boost in the pipes pushes OUT -- Side by side -- the cylinder goes up and down -- no amount of boost pressure can make the cylinder move. The wastegate probably has a brand name, relating to the KKK turbos - I'm not sure though.

If I were to disconnect my wastegate completely - Absolutely no lines going to it whatsoever -- I will only make 10psi of boost max. The pressure in the exhaust manifold overcomes the spring pressure on the wastegate, forcing the wastegate open. It was a failsafe design implemented by BMW to prevent overboost if anything messed up.

Is there a way you can plug up your bypass valve? I know you say boost can't open it, but if there's a rubber diaphrabm it won't need to open it, the boost will just go around it.

Based on what you're saying it sounds wastegate related though. Hard to tell if you have no leaks without actually experimenting... :/

Boris

TCD believes that I might have carbon deposits around the valve, I'll check it out whenever I can. It only takes a few minutes to remove the wastegate. I'll also check and see how hard it is to push the valve.

The spring may have worn out. Most wastegate springs do. One reason why the are usually servicable.

You might have blown the seals on your turbo.

Nah the turbo is still good, blows almost no oil, I checked the shaft play and it's non-existant. Only about 30k miles on the turbo -- still in wonderful condition.
But yes, it might be the spring - I'll find out this weekend when I diagnose it.

But then again, I'm starting to think it might be a vacuum leak. I have noticed that my normal idle vacuum leak of 20 is now more like 14. A drop like that would suggest a decent sized leak.

If thats the case then almost for sure you have a leak.

Ok -- I took off the wastegate -- and I'm almost sure it's the spring. I can compress the valve/spring with one hand without too much effort -- that says alot...

Ok -- I took off the wastegate -- and I'm almost sure it's the spring. I can compress the valve/spring with one hand without too much effort -- that says alot...

Not really, check the diaphram

Can't, it's all welded together - You can't disassemble them unless you are one hell of a welder.

Today I went and tried a spare, healthy wastegate - It behaved exactly the same as mine. I don't make 1psi of boost till 2500rpms, full boost around 4200. So the wastegate theory is ruled out.

Then I noticed that one of my exhaust manifold studs had completely backed out and was just barely hanging on without a nut. I re-installed it and put a nut on it. I then went through and tightened all of the other nuts only to find that I was missing ANOTHER nut, right next to the loose stud. (Which left 3 spots where the gasket was not tightened down -- 1 being a missing/broken exhaust stud in the head). So after tightening and replacing nuts, I put everything back together and took her for a spin.

Same thing 2500rpm = 1psi 4200=10psi (11 sometimes in 3rd)

I am so stumped....

I did a post throttle body vacuum check. Took the line off to my RRFPR and blew in -- it was making lots of noise in the intake manifold, I could blow through very easily. I pinched off the line to the IM and I couldn't blow at all. Unpinched and it blew easily. Is it supposed to be like that? Blown IM gasket?