Hi my 99 t6 accelerates very fast off the line and up to 4500-5000rpm, then it seems to flatten out is that normal? I thought the second turbo is supposed to work at higher rpm. I have new plugs and all cylinders are firing fine with no faulty codes.
Any suggestions?

 

Sounds like you're having the same problem I am. I just found out my catalytic converter came apart and ended up in my muffler. It got so hot it melted the inner fender wheel well. I would look to see how hot your muffler is. I had an issue with faulty o2 sensors, replaced them and no codes but flat line at 4500 rpm. Let me know what you find out.

 

[quote=hcmandog;286520]Sounds like you're having the same problem I am. I just found out my catalytic converter came apart and ended up in my muffler. It got so hot it melted the inner fender wheel well. I would look to see how hot your muffler is. I had an issue with faulty o2 sensors, replaced them and no codes but flat line at 4500 rpm. Let me know what you find out.[/qu

I am still trying to figure it out, It works well 80% of the time, it may be a old vaccuum hose.

 

i am also having that same issue with mine..it starts to loose boost at 4500