[nerfyo]

Hello, I have M57 bi turbo engine in e92 2007y .
After I bought car I went to dyno to check on what condition my engine is. After measurement, the lines said there is 295 HP which was nice. I did tunes - wagner fmic, replaced all injectors for new, deleted dpf/egr and I go for a tune. Result was 400 hp on stock turbos - for me awesome. I was driving like that for over an year and my smaller turbo said enough. I decided to regenerate it and also make a hybid from bigger one. My mechanic mount all parts, also changed timing chain (I don't know that this sentence is right , sry) and also all components like slides, tightener.

Going to the point, after all modifications I go for next tune for 400++ hp but on dyno, when the engine heats up after few runs, there was no boost till 3,000 rpms , which looks like, that small turbo is not building pressure and there was like 380 hp, so less before turbo change. When engine cool down, boost come back, and same situation on road, few pulls - no boost at low range of RPM.

I replaced all vacuum valves but it didn't solve the problem.

any ideas ?

[RS DAVE]

Check the ohms on the two control solenoids mine did the same thing, 1 had gone down. just replaced it and everything was back to normal.

[Yozh]

Check system vacuum at various points when your car is down on power. That will help diagnose. But I do agree that both pressure converters should be renewed if they are old.

[nerfyo]

hmmm, by control selenoids I think You mean those vaccum valves which I replaced. There were 4 valves controled by underpreassure I think.

[Yozh]

You need to test your whole vacuum system. If you replaced all the pressure converters and electric switchover valve, then you need to check your vacuum lines to make sure none are split or broken.