I have a 84 300td that has a lot less power than our 84 300d.
The car has a boost gauge and I haven't been able to get it to go above 4 psi, I check boost on a 5% grade with foot to the floor car goes 55 mph.
Things I have done:

- changed filters
- cleaned tank and screen
- cleaned banjo bolt on intake and alda
- run line from banjo direct to alda
- disconnect overboost line and check if valve was working with air
- adjust valves
- check cam timing, it was good
- set injection pump timing , it was retarded 3 degrees
- checked injectors, good spray and pop pressure
- turbo spins freely no damaged fins or excessive play
- turned uo alda 1/2 turn, got more low end and more smoke

After all this car runs smoother but still no top end and 4 psi max boost.

any suggestions?

Someone has a thread started today or yesterday saying the cleaned their waste gate and got more boost.

http://www.peachparts.com/shopforum/showthread.php?t=233347

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84 300D, 82 Volvo 244Gl Diesel

Remove the wastegate cover, push the diaphragm by hand and listen for a clear clunk as the valve seats when you let go. If it doesn't clunk or does not push back then its time to consider getting a used turbo.