You can make a tester to pressurize the whole boost circuit to a certain pressure. There's a pic of mine in my gallery, it's diagnosed many problems over the years.

 

That mounts to the flange where the intake is on the turbo, I assume?
Does it matter what pressure that you keep?

 

may not be your prob. but check your serp. belt i had some craks on mine that i didnt think were all that but still whistled and only at certain temps. new belt no whistle

 

Belt is new. I don't think that is the problem.

 

are you sure its not the turbo silencer ring?
just checkin.....

 

It makes the noise with or without the ring in. So, it's not that.
I made an adapter to pressure test the air induction system. I just need to get out there and check it, but it snowed all yesterday afternoon, and I don't have a nice, warm garage to work in.
I have noticed that the warmer the day is, the more power I have. The colder the temps, the less power. Not a big difference, but noticable. Did I read somewhere that this has to do with timing advance in the injection pump, or something like that, or is it indicative of a problem, and is it possibly related?
And, if the wastegate isn't working as it should, could that cause some of the problem? If it doesn't function and fully travel, can it be bleeding off some of my boost?
I know- get a boost guage. I haven't gotten paid in over a month (About $15,000 out there, already billed, waiting for it to come in), so I won't be spending the money for now.

 

kinda sounds like an air leak; easy way to figure that out is the old trick of spraying brake parts cleaner around the head, hoses & rubber lines while its running, (be careful spraying it near the exhaust :-), & if it makes the idle go up or down you've found a leak.
I had a ford idi turbo diesel a few yrs ago, & the thick rubber elbow at the turbo had a hole in it, but you couldn't tell unless the pressure was built up...
let us know what you find

 

It did it some more today, so I messed with it a little. It happens at full throttle, while under load, such as pulling an incline. The truck shifted, changing the RPM's, which did not change the noise. I could back off the throttle a little and it would go away, then back on the throttle full and it would come back. As soon as it stops pulling hard, it quits.
It sounds like a cross between a whistle and a high modulation vibration. As soon as I can, I will pressure test the intercooler system.

 

id almost bet money its an air leak. just by what you described there. under full load is when your boost will max out. i think your wastegate is fine if its not working your boost wud be even greater. unless its stuck open in which case you wudnt build nearly as much boost. get that adapter and some air psi in that intake system and see what you can come up with

 

This might sound silly, BUT, I had and old gasser that would whistle on and off ,load and temp variable,It turned out to be the fan clutch.

 

Hmm... sounds interesting, but now that I think about it, it seems like it would go away when the truck shifted, thus dropping the rpm's. And, the noise would'nt be linked to minute changes in the throttle input.
Is it possible that the noise could be inside the injection pump? If so, wouldn't it change when the truck shifted? Isn't the pump rpm's linked directly to the rpm's of the engine?

 

Yes, it attaches to the front of the turbo, in place of the duct from the air cleaner. I will usually pressurize the system to approximately whatever boost pressure the engine is at when the noise occurs, or about 20 psi which is safe but high enough to show up any leakage.
Sometimes you will have to bar the engine around a bit to get enough valves closed to hold the pressure.

 

Well, to freshen the post, I will report on what I do know (what isn't causing the whistle)-
1) No intake leak
2) Can't be fan clutch or injection pump- sound doesn't change with RPM drop
3) No play in the turbo

 

I pressure tested the intercooler system today. No leaks or whistle. So, my next plan is to investigate the wastegate. It will need to dry up some outside, or I will have to find a place to work before I do that.

 

pinch it off (if its a rubber line) and take it for a spin if you can duplicate the conditions it acts up in that wud be 90% conclusive in my book