Sounds like a blockage to me but I know almost nothing about diesels.
More info here to read http://www.littlepowershop.com/60problems.html
The next thing you may have read or heard about is the egr cooler and/or valve. This system is just a nightmare on these trucks. For emission purposes the engineers designed a system to reintroduce exhaust gases into the intake manifold to be reburnt. Exhaust Gas Recirculation. While I suppose it must have met whatever standard for emissions that they had to meet, it is a nightmare for any one who owns these trucks. At the very least sooner or later your egr valve will either become completely clogged up with soot and quit working or just plain fail. Which leads to terrible running that commonly gets misdiagnosed as bad injectors, faulty FICMs, bad turbos, or a host of other shade tree guesses. How the egr system works is as follows. The hot exhaust gas is let into the egr cooler from a pipe between the exhaust manifold and the turbo. This exhaust has a temperature anywhere between 400-1400 degrees. In order to cool the gas before introducing it into the intake, they have coolant running through the egr cooler to exchange the heat. On the other end of the egr cooler is the egr valve. This valve opens to let exhaust gas into the intake manifold when the pcm decides conditions are proper to do so. The major problems with this system are two fold. First, dirty sooty exhaust gas is being blasted into your intake tract. The soot covers everything in it’s path. It is not unusual for us to tear down a motor that has had it’s egr system intact it’s whole life and find the intake ports into the head to be coked up to half their diameter. The intake manifold becomes restricted from this coking as well. But that is not the worst problem. The extreme heat acts on the cooler and breaks it down. Sooner or later it will rupture either letting coolant into the exhaust or intake. (lot’s of misdiagnosed head gaskets here since fluid can run into the cylinder once you shut the engine off and hyrdolock it up) Really bad leaks let exhaust pressure into the coolant system. Which if not taken care of quickly can and will result in blown head gaskets. But wait there’s more. The extreme heat that the coolant is trying to scrub away in a normal functioning egr system breaks down the coolant. Some of the components of the coolant start turning into a goo like substance that does a really nice job of clogging up all sorts of coolant related parts. If you have been doing any research about these engines you have no doubt heard about replacing the oil cooler. These need replaced because this goo will clog them up. Oil temps will then be elevated causing quick overheating when the engine is worked. Also, the coolant leaves the oil cooler and continues to the egr cooler next. If the oil cooler is restricted, your egr cooler will not get enough coolant flow to keep it cool. Next thing you know, blown egr cooler. Then of course a shop diagnoses the bad egr cooler, replaces it, and the customer comes back in a month with another blown egr cooler. It is not unusual for us to get trucks that have had six or seven egr coolers replaced in their lifetime and never an oil cooler. This is the kind of stuff that gives these engines a bad name and it stems from the people working on them misdiagnosing them and not doing complete repairs. My advice to you would be to delete the egr cooler out as soon as possible and replace the oil cooler if you have more than 50,000 miles on the truck when you do it. At the very least, if you have to have the egr system functioning, replace the cooler with a bullet proof one that has a very robust center section that will not rupture. Adding a coolant filter to every engine is also a great way to combat coolant contamination and is a must.
And lastly, no 6.0 problem article would be complete without touching on turbos. I cannot stress enough how often the turbo gets blamed for poor performance when there is absolutely nothing wrong with it. Here are just a few misdiagnosed bad turbos from the last week. One guy heard a pop and lost all boost pressure. No smoke, no oil leaking anywhere, but lost all his power. “The turbo isn’t working. My mechanic says I need a new turbo.” After talking with the guy for a few minutes I found out an intercooler boot had come off. I advised him to fix it first and he was on his way. The second one was a customer who had the turbo replaced not once but twice and now the second one was bad after two weeks. Come to find out his exhaust backpressure tube was completely plugged. Since the pcm uses exhaust backpressure to command the turbo to open and close down the exhaust side and wasn’t getting good feedback, the turbo performance was erratic. No turbo needed there either. We had a guy with a blown intercooler that had been misdiagnosed. There was another with a sticking egr valve that was calling for a new turbo. All those people were going to buy or did buy a turbo when they absolutely did not need one. Turbos are another item on 6.0 Powerstrokes that I hear, “Those engines are junk. I had to put six turbos on it since I have owned it.” No you didn’t. You paid your mechanic to put six turbos on it and the sixth time he actually noticed what else was wrong in the first place.
Here is how to see if you turbo is bad: Take the inlet from the air cleaner off the turbo. You will be able to see the compressor wheel. Grab the end of the shaft with your fingers. Does it spin freely without coming to a sudden abrupt stop? If it spins good, it’s good. When you have a hold of the shaft, try and move it side to side and then in and out. Some minor play is acceptable. It’s hard to describe exactly how much play is ok to someone who hasn’t worked with many turbos. The best I can do is this: If it feels like it is moving back and forth against a uniform bearing, it is probably ok. If you are picking the shaft up from the bottom and it falls back down when you let go, the bearings are probably out of it or worse. The other test for the turbo needs to be done with a scan tool. With a scan tool you actuate the valve that moves the variable veins in the exhaust side of the turbo. You should hear the exhaust tone change and see a fluctuation in back pressure. If nothing happens, either the actuator is bad or it is possible the variable veins in the exhaust side of the turbo are coked up and need cleaning. This can be done by removing the turbo. Disassemble the exhaust housing and clean the rust and soot out of there.
If you are having a problem that is diagnosed as a bad turbo check the shaft play and turbo actuation first. If both of those are ok, you do not need a turbo. Only good diagnostics will find the real problem. A turbo isn’t a mystical device. It is much more like a wind mill. If it is not spinning and not broke, there may be no wind. If it is spinning but not producing any power, it may not be connected on the output side.