Quote:

---

The only thing that's even close to suspect was the short length of rubber tube to the wastegate. It was pretty crumbly and looked like it had taken some heat.

---

If the vacuum line to the wastegate is bad it will cause your problems.

That line pushes manifold pressure to the wastegate. If you were to pull it off, the wastegate would never open. That means the turbo would not stop making boost until the computer shut down the fuel or the pistons melted.

The wastegate has a spring pushing on a diaphragm. That's what holds it closed and makes the exhaust go through the turbo.
That vacuum line sends manifold pressure to the other side of the diaphragm. It pushes against the spring.
When the turbo spools up it will send boost pressure to fight that spring. Once the boost is stronger than the spring it forces the wastegate open and exhaust take a shortcut around the turbo. Boost pressures drop. Wastegate closes. More boost is made. Vicious cycle.

Under load, the boost pressure in that "vacuum" line and the spring come to a bit of an agreement. They balance one another and hold the boost steady. Very simple and rather ingenious. Self regulating.





An old trick to sneak more boost was to bleed a wee tiny bit of air out of the wastegate vacuum line. Doing this dropped the pressure on the back side of the WG. That means the turbo had to make more boost to overcome the WG spring.
Other guys cut the WG rod, threaded the two pieces, and slipped them together with a long nut. That let them adjust it like a tie rod.

Both of those things will upset the computer. It is programmed to shut down the fuel when the boost gets higher than allowed.