I've read through the detailed description of how the sequential turbo system works. I now have a general idea of how each of the mechanical pieces play a roll to give a healthy 10-8-10 boost pattern. However, I am getting an inverse result after making a fix and its throwing me off a bit. I can use your help!

When I purchased the car, the Boost Pattern was as such:
10-0-0

The car will make boost with the primary turbo. Right at 4,500 RPM, boost would flat out to 0-1psi and stay there till red line.

I looked inside the engine bay and found a vacuum hose that had 1 end connected to one of the ports on the intake manifold. Looking from the top, it is connected to the 3rd outlet. Looking at the diagram below, it looks like it is connected to one of the 4 hoses next to the PCV Valve by the Intake Manifold (Purple, Maroon, Orange, Green).



The other end was not connected to anything. I started looking around to see if there was anywhere it may have popped off of, and I found an open plug right next to the Charge Relieve valve by the Secondary Turbo. In the diagram above, it is the Green line with the Purple dots. Here is a picture of the open plug:



The hose was also the perfect length to fit into the plug. I figured since there is an open plug that is connected to the air side of the secondary turbo, this can explain that the boost is leaking when the secondary turbo kicks in, which is responsible for the boost loss after 4,500 RPM. I plug the hose into the open nipple and take it out for a spin.

Now, I am seeing an inverse result. I have 0 boost until 4,500 RPM. After 4,500, I hit my 10 PSI boost all the way to red line.

IF the hose is not connected to anything AND if the secondary turbos intake side plug is left open,
THEN I have boost from the primary turbo, but boost drops to 0psi after 4,500 RPM to red line.

IF the hose is connected to the open plug on the secondary turbos intake side, then I have 0 boost until 4,500, and then I have 10psi from 4500rpm to red line.

I was left with 1 possible choice: Leave the hose disconnected from the plug, AND close the plug on the secondary turbo to prevent any boost leak. I tried this and I had the same result as if the hose is disconnected. I have boost from the primary turbo until 4,500 RPM, and after 4,500 to red line is a flat 0.

I've looked at the diagram and I couldn't find any hose that connects directly from the bunch where the intake manifold is directly to the secondary turbos intake side. I've also tried looking at simplified versions of hose setup, and couldn't find anything there.

The inverse result after attaching the house to the secondary turbo just threw me off. Any ideas as to what's going on?

 

I'm not an FD guy so not so familiar with the system but I would start by inspecting the check valve to the pressure tank and your solenoid valves particularly valve F since it leads to the hose you suspect to be causing the problem.

 

sounds like some of the hoses right above the turbos are misrouted, keeping the charge relief valve open when it should remain closed.

follow the diagram and check all connections through the lower intake manifold.

if the charge relief and the charge control lines are backwards then i could foresee this problem. the charge control butterfly should be open at the 4500 transition, it remains closed below that.

top - yellow goes to EGR
2nd - dark green goes to rear nipple on charge pipe(in your picture)
3rd - orange goes to the charge relief valve, the rear blowoff valve
bottom - light green goes to the charge control actuator(butterfly valve inside the charge pipe which blocks primary from secondary turbo)


you could also simply remove the hose from the charge relief valve and see how the turbos react. this should keep the valve always closed but the transition will be slightly laggy. if there is an issue with the charge control circuit then this probably will not change anything.

 

Thank you for the write up! I followed your directions and found that 3 of the 4 hoses were misrouted. The top hose (EGR) was the only one routed correctly. The remaining 3 below were routed incorrectly.

The car is now driving much smoother and even picking up boost at a lower RPM. This is the first time I felt the kick of the 10-8-10 transition. Was midway on a turn. I nearly shat myself!

Thanks for your help! Now I have to figure out how to sort out CEL code 5 and 16.