'01 6.0l issues....

Ok, here we go!! I have recently come across a 2001 3500 with the 6.0l with a whopping 251,000 mi. Going into this, I knew I was going to have some work in front of me, I just need a little help with where I should start!
I was told that one of the cylinders was "dead." I guess it has lost compression and they felt it was either cylinder #7 or #8. The truck does run, rough at that, but it will run and get up to speed. It smokes while speeding up but will clear up when at speed. (I found this out trying to get it home) Some have said that they feel that it may have a hole in the piston, while others feel that it is a valve issue, and the rest say it has to be a bad head or head gasket. (I have not seen any coolant in the oil)
My question is - where do I start? Should I pull the head off and see what I see? If it is a valve that is not seating correctly, will the Sea Foam treatment do anything to get the carbon out?? I don't want to dump a lot of cash into a motor with a whole lot of miles on it but I do like the truck!!

Start with the basics, a compression test on the suspect cylinders.

Sounds good. I will be spending tomorrow looking it over and post any new finding as soon as I get them!

pull the valve cover. get ready for a lot of oil going every ware. turn the truck on and watch the rear valves on the side you think your having truble on. chevys are good for the lobs to ware on the cam. if the valve is not oping and closing right your not going to get a compression test that is reliable.

Well, after a day of work, this is where I stand. The first thing I did was tested the compression on all cylinders. I found that the #2 cylinder has about 30 psi of compression. The rest were about 85-90psi. From what I found in the tear down manual, they recommend no less than 100 psi per cylinder. I also pulled the valve cover and with all the oil flying, they all seemed to be moving. I then decided it is time to dig alittle deeper. As of now I have the intake off and when I get another day off I will keep going to the heads. I have called to get the head gasket set and the parts stores are saying there are two types of valve seats. How do I know what to get?? One answer was to look at it when I get the head off. It looks as though one is a two piece seat and the other is one peice. Hmmmm....

if you only have approximately 30psi compression on cylinder 2, then i would suspect that cylinder, possibly broken ring, hole in the piston, something like that.

Ok, I know it has been awhile.. I found my problem! As you said, it was a broken piston. I pulled the right head off and there it was! The #2 piston had the outside chipped off above the top ring. All new pistons and rings and a bunch of new gaskets and I just buttoned it up.
Now a new issue. In lieu of starting a new thread, I'd like to see what you think. I have it all back together, added some oil and gave it a crank. It stated up, but after about 10 sec. I had no oil pressure. I shut it down and looked it over. No big puddles under the truck as of now. I looked over the wires and it all seems to be connected. So, I started it up to see what happens, and after another few seconds, still no pressure. The needle didn't move a bit and the oil pressure light stayed on. I then pulled the oil filter off and sure enough, not a drop of oil in the filter.
Is their something I need to purge or bleed to get the air out of the system? I did nothing with the oil system with the exception of taking the pickup tube off when I took the oil pan off.

The pump may have lost it's prime, fill the oil filter with oil, which you should do anytime you change oil and retry it.

Sounds good. I will give that a try on Wed. and see what happens. I will also keep that in mind for future oil changes. I usually just let it fill itself when I start the motor.

Sounds good. I will give that a try on Wed. and see what happens. I will also keep that in mind for future oil changes. I usually just let it fill itself when I start the motor.

with the spark plugs removed and the fuel pump disabled I would crank it several times ,,this will help get the oil flowing ...then set up for a run test ..

with this type I don't know how to prime the oil pump ...

Well after trying the above suggestions, I am in the same position. I filled the oil filter, took the plugs out, cranked it over and put the plugs back in. It started back up, and still no oil pressure. Now I am officially lost!!

There was an episode of HorsePower TV where they built a Gen III small block only to have very low oil pressure on the Dyno. IIRC, it was the pickup tube at the oil pump. The O ring was crushed and they pulled the pan to fix it.

Here are some pictures of the O Ring and Pickup tube. http://www.ls1howto.com/index.php?article=4

//2000CAYukon

I guess that's the only thing left to look at. I guess I will drain the oil and look it over again. I'll keep you posted!

Once again, your right on. I pulled the oil pan off and my o-ring was trashed. I put it back together with a nice $12 replacement from the dealer and it's got all kind of pressure.
Now that it runs, the fine tuning..
I have found that so far it idles pretty rough. After a min or so, I am getting a check engine light. My nifty little scanner says that I have "misfires on multiable cylinders." I can reset it, but it goes right back. At higher RPM's it has really smoothed out. I took it into work for a little more complex scan. I am getting high numbers of misfires at an idle on #2 and #6 cylinders. I tried to research it on the scanner and its showing that this could be an injector issue. I tried moving the wires to the injectors and no change. I also just replaced the spark plugs so I have ruled that out. I tried moving the plug wires to other cylinders and also no change. I even traded the coil packs to other cylinders and no change. It also mentions "bad fuel" as a possible cause. I have a feeling that the fuel is no less than a year and a half old. I added fuel additive a couple days ago to try and reduce the water in the fuel. Would this not cause a misfire in all cylinders, not just two?

It also mentions "bad fuel" as a possible cause. I have a feeling that the fuel is no less than a year and a half old. I added fuel additive a couple days ago to try and reduce the water in the fuel. Would this not cause a misfire in all cylinders, not just two?

you must drain out the old fuel it is bad ...being a boater this is one thing that you know , old gas is bad gas ....one way to keep gas good up to 2 years is if you use the stabilizer at the higher concentrations ...

I would then replace the fuel filter and add 4 oz. of marvel mystery oil to the NEW fuel and see if it runs better ...if not check the fuel pressure using the testing proceedure..hopefully the injectors are not messed up...

now what to do with that old gas ???? lawn mower ??

Ok, after all this time, I am on the road again!! I would like to thank everyone for all the help, you truely are a life (and money) savers! I am still getting a service engine soon light once in a while, but it's a bad O2 sensor. For what I have done, that should be a pretty straight forward fix. Thanks again everyone!