I removed the downpipe/cat today, and the boost is much improved. Apparently the cat was plugged and causing quite a restriction. I'll definitely use some sort of anti-seize when replacing the downpipe though, as removing one of the studs (the nut froze onto it) required 5 hours of work, and eventually required an angle grinder to slice off (very VERY little room to work with too).

I drove it today without any exhaust system whatsoever. It was loud, but the boost hit 9.5psi (up from less than 7 before cat removal) and the car took off like a ROCKET (relatively) once boost peaked. There is definitely a problem though. With the wastegate signal completely disconnected (i.e. wastegate rendered inoperable) the max boost was 9.5psi. With no exhaust restriction, and no wastegate input, I expect that boost would have continued to skyrocket until the (now modified to 13psi) fuel cutoff hit. This didn't happen. The car ran flat out through the first two gears (AW70 tranny) at full boost, and after quickly raising to it's 9.5psi peak, it stayed there the whole time.

I don't know how to really check if the wastegate isn't closing completely, but the linkage operates freely when I checked it today. Is there some way to make sure it's fully sealing and not bypassing exhaust gas? Is there some bizarre system in my car that could prevent boost from going over 9.5 that I don't know about? Like I said, I adjusted the fuel cutoff to 13psi, so it shouldn't be that. The red 'TURBO' light did flash a couple of times at max boost, could this indicate anything going on? Any ideas on why the boost isn't going higher? The turbo is a recent replacement, so it shouldn't be broken. Thank you for any help you have to give.
--
Isaac Babcock - '83 245DL 'Borkie' and '83 244 turbo project