I'll keep checking but at this point I hate to assume, but it seems as the wastegate, possibly the spring broke. This would explain the "all of a suddeness" of the problems occurrence and the lack of boost. If a ring or two on the spring broke, the wastegate would always be open. the louder turbo whine/whistle could be from the wastegate being "just" open enough.

I ran compressed air through the manifold to check for leaks in the plumbing and found none. I long ago deleted the EGR and associated plumbing, so at this point I'm left with the turbo assembly as my most likely source.

I guess the only way to find out is to disassemble the wastegate. I hear that the Garrett ones are a PIA, any links or tips from those who have done one?

Also with respect to source for parts, where can I get a replacement spring? Would a generic wastegate spring from Summit work in a retrofit? Would a different wastegate actuator work in this application?

TIA

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)