ok .. I have problems with boost on the second turbo
stock 1992 mazda rx7 fd3s Twin Turbo
Here are my syphomas:

1. after 4800 rpm the boost pressure drops to 0.4 bar
2. when I have 5000 rpm or more (pressure 0.4 bar) and for a moment I will release the gas pedal and then press it again, the boost pressure on the secondary turbo drops to 0.1 bar
3. when it changes gear so that in the next gear (for example from 2 to 3 gear) will rev higher than 5,000, the boost pressure is 0.1 bar

I am asking for help because I have been struggling with it for some time and unfortunately I have not found a solution.

What I did
1. I replaced all the vacuum lines
2. I exchanged solenoids in the rat form
3. I regenerated the turbines (I had the same symptoms on different sets of turbines)
4. I replaced all engine gasket seals with new ones

 

You're going to have to step through the turbo troubleshooting guide. Have you replaced the check valves? Does the pressure tank hold pressure?

Dale