Nov 26, 2012 // Turbo Essentials //
One of the unique new features of the MKiV Supra was the Twin Turbo Sequential operation. Only a handful of cars touted this Sequential System. The system was designed to provide greater power levels at lower RPMs by diverting all the exhaust energies to the front #1 turbo. Since these turbo’s are rather small, running on one turbo provided a high spool characteristic. At or around 4000 rpms, the rear #2 turbo would kick in to provide for the peak potential power.
With this unique system comes complications. There are a lot of components that go into this system. If any of them malfunction, the entire system goes down. The “orchestration” of Actuators, Vacuum Switching Valves (VSVs), and vacuum lines via the ECU is a
real feat. As our beloved MKiV Supra ages, so does the Sequential System. Vacuum lines become brittle, actuators lose there ability to hold pressure, VSVs start to break down, Pressure tank loses it’s ability to store pressurized air. All of which is needed to have the system work.
Understanding this system can be somewhat complicated and difficult to diagnose. Several years ago I wrote a diagnostic manual to help people try to understand how it works and help find issues. http://97supraturbo.com/public_html/Seq%20FAQ/Seq%20FAQ.doc This doesn’t cover 100% of all possible issues, but it covers the most common. If anyone is serious to understanding and diagnosing the Sequential System, I highly recommend to purchase a MityVac hand pump. Like the MV8510 series. http://www.lincolnindustrial.com/asp/distributors/access/distributors/4_MV8510%20PIS.pdf. You will be able to test all the components with this. Find leaks, and actuator healthiness. As well as testing the pressure tank.
This all should aid you into figuring out issues. Your going to find that there is not many dealers/repair places out there that can understand and repair effectively, so the only person that can really get to it and fix things is YOU! Good Luck.