98 6.5 turbo
 

was wondering if I should try pinching off the vac line to the waste gate for more power?
truck seems to blow black smoke under tow and loss of power?
no leeks on the cross over pipe, runs strong when not in tow.
any help please?

pinching it off would mean the wastegate would be open all the time. you need to wire the wastegate shut but dont tow with it because the boost could be harmful to the engine

You likely have a leak in the vacuum lines that provide vacuum to shut the wastegate. Easy fix.

where do I start and what do I look for, there is vacuum at the line with a good pull?

Just follow the vacuum lines backwards from the turbo checking for any cracking at all, or to see if they've come apart. Just takes a little time.

how do I find the leek tried everything? where to look?

see any cracks in the plastic?

Rick
look at the arm on the wast gate with engine off then start it and look at the arm if pull up then screwdrive try pushing down on wast gate arm if you can't most likey there no vacuum leak and if that arm don't move when starting the truck try tapping on the Wastegate solenoid they get stuck

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other thing i don't know what mods you have done to truck or how many miles on it maybe clog cat that cause loss of power