3406E problem driving me crazy-long story

I have a 98 379 with a 475 1LW 3406E. The manifold pressure is what I consider low, typically 21lbs when pulling hard sometimes a little more. Since I bought the truck, there has been a underlying whine coming from the turbo like when you pinch the end of a balloon and let the air out. This is in addition to the normal noise you would expect from a turbo. I have had the truck about 9 months and put roughly 90,000 on it since I got it. Recently this noise has become more pronounced. My first thought was the charge air cooler, I made up some caps, plugged it off and put 30lbs pressure in it. I let it sit for over 45 minutes and it did not lose any pressure. I found a tiny hole in one of the hoses between the cooler and the engine so I pulled off the other three and checked them all. I replaced 2 of them keeping the other old one for a spare. We pulled the elbow off the turbo output going to the air to air cooler and the 2 o-rings looked pretty bad so I replaced them. I have checked the little silicone hose that goes to the wastegate and it is OK. I also checked the diaphraghm on the waste gate acutator. I tried running it with the hose to the wastegate blocked off. I got a little more pressure then but not much and no real change in the noise. The only thing that really changed the sound of the noise was when I changed the o-rings on the elbow. It didn't get any quieter but it seems like the pitch might have got higher--maybe--I have been listening too hard. I checked the elbow and turbo housing for cracks and did not see anything. I found 2 of the bolts that hold the turbo to the manifold loose so I replaced them all with the correct bolts and replaced the gasket. I have also checked for cracks in the manifold and other exhaust leaks. I am going to be home tomorrow, I think I am going to disconnect the hose between the turbo and air to air cooler and plug the output from the turbo and just drive it up my driveway and see if the noise is still there. Just revving the engine up with no load will not prodouce the noise because it won't build enough boost without a load against it. It does not really start until there is about 10lbs of manifold pressure. I might pressurize the cooler again just to double check. I have also pulled the housing off the turbo and checked for signs of the impeller rubbing the housing, not it either. The bearings on the shaft and good and tight and little if any play, no signs of it pumping oil either. It sounds like its coming from the right side of the engine while driving it, I have even put the cruise on and sat in the passenger seat with my head out the window trying to hear it better. This thing is driving me nuts. My other truck has a 3406B with a warmed over pump and it would outpull this one any day. It also only gets 5.5 mpg on a good day and I don't think I have ever gone under 6 with the E model. It usually gets 6.2-6.3 and I have gotten as high as 6.8 I bet it would even do better if it ran right. Its completely stock and had a o'haul by Cat about 350k ago. I am starting to wonder if the clearance between the impeller wheel and the housing is too much or maybe a problem with the air compressor? Any ideas or similar experiences would be welcome. All I know for sure is its driving me nuts. What do y'all think?

 

The couplers are what I called the hoses. I did find a very small hole in one of them. I put 2 new ones on and put them on the turbo side because I thought they might get a little hotter on that side. When I pressurized the cooler I put my plugs in the couplers where they hook to the turbo and to the engine so I was putting pressure against all 4 couplers, the metal tubes and the cooler itself. I put it up to 30 and had no leak during the 45+ minutes it was under pressure. I'm a little nervous about putting 60lbs against it incase one of the plugs blows out, that would be pretty scary unless I can figure out a way to catch them if they blow out, some kind of safety chain or something 30 pounds had me a little nervous, I just kind of gradually got the pressure up until I reached 30. I was looking at the impeller wheel and it is not damaged but I too was wondering if it is just worn from use. I know from the paperwork I got with the truck it was not replaced when CAT did the overhaul but was inspected and deemed ok to use so there is no telling how many miles are on it. When I had the waste gate blocked off I got close to 30 psi of boost but it was not steady like it should be. I have a friend with a KW that has a 5EK 475 and he gets close to 30lbs of boost with his. I have another friend with a newer 550 and he tells me the same thing 27-29lbs. I think that by putting the plug in the output side of the turbo, if it still makes the noise then it pretty much must be a bad turbo? Also I checked the play side to side up and down and fore and aft. It seems pretty tight, like if I was guessing less than .020 any direction you wiggle it. I has so little play you almost can't feel any I had one on a Cummins I used to have that I swore moved up and down at least 1/8 inch and it ran quiet and never had a problem. Thanks for the input. I am staying home until I find a good paying load so I might have a lot of time to figure out what is wrong.

 

Thanks, I will add that to my things I am checking out tomorrow. I have sprayed ether all around with the engine running at idle trying to find a leak on the intake so far no luck. Tomorrows another day thought and hopefully I will figure it out. I am starting to think worn impeller wheel. As far as mileage goes, mid 6's in not horrible for a 379 I don't think. I pull flatbed 95% of the time and usually close to gross. I am going to try calling Caterpillar in the morning to see if there is a spec for the vanes, maybe I can measure them and see if they are worn. They are usually not that helpful, they just want you to bring the truck in. Thanks

 

Update:
What I did today,

1. Removed line from head to compressor and plugged it off. First on the side going to the head and then where the line goes into the compressor thus ruling out a bad hose or a bad compressor. Its a #10 Aeroquip hose like hydraulic lines are made from.
Drove truck, Not the problem.
2. Pulled off air intake boot from filter to turbo intake.
Drove truck, Not the problem.
3. Pulled hose off turbo discharge that goes to charge air cooler and plugged it so the turbo still built pressure but did not pressurize the whole intake system.
Drove truck, Not the problem.
4. Put hose back on turbo and pulled hose off where air charge goes into the engine and plugged it so now the whole intake system and air charge cooler is building pressure but not putting it into the engine.
Drove truck, Not the problem.
5. 3406E does not have an intake manifold. I pulled the bolts holding the air intake horn onto the head. They were not really very tight but not overly loose either. Gasket looked good. The pipe plug mentioned earlier in this thread was also not really loose but not very tight either and had no sealant on it. I put some thread dope on the plug and tightened it up and then put a small amount of Ultra-Blue silicone on both sides of the old gasket and after it tacked up for about 15 minutes I put it all back together and went in the house to eat dinner.
I actually got a good paying load to haul tomorrow so I guess I am going to Kansas. I am going to leave early enough so that if the noise is still there I can run it by a guy's shop up in Denver and have him take a ride and see what he thinks before I leave town.
I also pulled the fitting out of the head for the boost gauge and plugged it thinking maybe the line to the gauge was bad. While I was at it I checked the sensors in the head to see if they were loose, they wern't.
I will have my laptop in the truck and will try to update Friday night.
Thanks to all for the suggestions and ideas.
Mark in Colorado