Very loud under load

Mine is doing that... ISX... not a Cat, but the problem may be the same--a broken exhaust manifold bolt.

The bolt was still in the hole and nothing looked out of order. That is, until I described the problem and our shop guy took a magnet to the bolts--one pulled out--broken.

 

Maybe it's the bolts or gasket where the intake elbow attaches. I had that very problem on an old A model Cat. It would be OK till just about the top of a long hill. There would be a pop, then you could hear the turbo spooling and air rushing out. Everything looked perfect. The mechanic just happened to grab a wrench and check the bolts, and two were loose.

 

No, because if you dont have boost pressure you wont have drive pressure either so it may not leak. Look for soot around the exhaust gkts.

 

The ISX has a variable turbo that builds boost even under no load if I understand it correctly. Mine will whistle at full throttle under no load as long as the air tanks are over 70 lbs. (Turbo doesn't spool until it has air)
Although mine isn't fixed yet, we've got a few of these ISX powered Volvos that have had the same thing go wrong. Our shop guy knew what it was instantly.

 

I have the same problem, loud whistlin noise on the right side, by turbo on my ISX. Dealer told me to replace exhaust manifold gasket. So I went to my mechanic shop got it done, put new of course exhaust manifold bolts. Noise didnt go away. So now dealer tells me to change the turbo, but you know how much these cummins turbos cost... 2500-3000. I cant just keep buying parts that arent cheap. If I knew for sure its turbo problem then I'd buy it.

 

if we sugest "hot side leak" there will be black deposits of ash from exaust gas. it is not dificult to find!

 

If you can pull out on the shaft and the compressor wheel scrapes the housing as you rotate it then the thrust bearing is gone. The compressor wheel is causing the noise as it rubs against the housing and it will get loader as the boost goes up.