My truck is loosing boost under full throttle. when i get in it it builds boost to about 25psi and then Drops. My truck then blows all kinds off black smoke. I did a boost leak test and all of my boots are good. I am thinking maybe a bad waistgate.

 

Sounds more like your air cleaner is plugged?

 

So, maybe it is sucking it flat

 

What mods do you have?

You might just be maxed out on a stock turbo...

 

How is your 351cw set up? Spring gate or?

 

Without knowing the setup, it sounds like the wastegate is releasing boost.

 

When I've experienced this problem (boost goes up and then drops to about 20 psi) I've always found it to be a fuel filter that's clogged up with whatever. A fuel starved engine can't make boost like it normally does. I'll first try bleeding any water in the fuel filter canister and see if that cures it but usually it requires a filter change to fix the problem. After replacing the filter (and getting the truck started and any air in the lines purged) I can take it out and punch it and it holds a solid 29-30 psi boost (good for tune level and my elevation of nearly 7000 ft). Just looking at the old filter won't necessarily indicate it's blocking fuel flow, but once the new filter is in place you'll feel the difference.

 

I read that again, deleted my bad info. I thought fuel delivery too, but rolling coal when the boost drops sorta disputes that.

Kinda sounds like symptoms of a soft connection boost leak. As in pipe boots. Sometimes they sound like a cat in the belts, but sometimes not.

I doubt the WG, since by design their performance doesn't fluctuate much. Even with dramatic failures I wouldn't expect fluctuations.