Knocking and blowing black smoke then white

[KarlLLY]

My wife and I were headed back from about a 1.0 hour highway trip. I had been running about 70mph the whole time. I cam off on to a side road and was going about 35 mph. then the truck starting knocking real loud and blowing black smoke out that quickly went to pure white smoke clouds. Truck was running bad let off the pedal and all went away. Pressed on the pedal lightly no problem. Press on the pedal a little heavy and all the knocking and smoking came back. Temp at 180 oil press at 50 no engine light on. Truck idles smooth. I just bought this truck and do not know much about it. It is a 2006 2500 cc/sb LLY engine 6speed auto trans 120k miles on it.
Any ideas would be greatly appreciated!

 

[TeaBagger2006]

have you checked all your boost pipes/fittings. seems like you lost boost pressure

 

[KarlLLY]

No I have not checked anything at this point. I called the dealer I bought it from and they asked me to bring it back over to them tonight. so I just night dropped it for them to check out Monday morning. They are a used car dealer not a gm dealer so I want to make sure they do not feed me some bs story about what is wrong. I have put about 600 miles on it in the last week with no troubles at all. I towed my 8k lb travel trailer with it and about a 10k load of wood with no troubles a few days ago.
Thanks

 

[Diesel Technology Source]

Does it do it at a certian RPM? If you can duplicate every time and it is at RPM then it may be the egr cooler has a leak and it is getting into the combustion chamber. Easy to replace it or better to delete it!

 

[MACKIN]

I would also check the balance rates my you have a injector sticking or going south. Black ,white smoke indicates excessive fueling.

Good luck

 

[KarlLLY]

Update: The used car dealer has had it for two days now and they have not found any problem. They say the truck is running great and having no problems for them. They are keeping it for one more day at this point.

 

[PhilsLB7]

Update: The used car dealer has had it for two days now and they have not found any problem. They say the truck is running great and having no problems for them. They are keeping it for one more day at this point.

I would have them go on a test run with you before you take it home. Try to recreate the problem if you can.

 

[KarlLLY]

I told them this morning that if they can not find a problem I want it in writing that if there is a problem in the next several months that they will fix what ever it is free of charge to me. I did not get a straight answer back from them yet. I am also thinking I may take it over to my local GM dealer and pay them to check it over. I will test drive it with the owner if they do not find anything. He called me late yesterday to ask if I was ok with him taking it home last night and driving it around some. I told him yes! I will keep this updated and thanks for all the input!

 

[Chevy1925]

Im puttin my money on a plugged fuel fliter. mine did the same thing your talkin about. under a light load, she ran great. start givin the juice after runnin for a while and boom. it was blowing a greyish smoke though. the truck would fall flat, almost die, and smoked like a freight train. put a new fuel filter on and hasnt done it for 30k since

 

[KarlLLY]

Update: They have now had the truck for 6 days. They now say that it might be a injector problem and they want to send the truck to another shop to have them check it out. They say there tech is not able to do anymore. I thought all the injector problems were with the early duramax engine (lb7 I think) Does anyone know if there are still problems with injectors on the LLY and up engines?

 

[KarlLLY]

Update I picked the truck back up last night. The new shop they took it to said that they can find nothing wrong with the truck. No codes and seems to run good. They also did a coolant dye & press test and a injector cut out test no problems found. They put a can of fuel treatment in it and said it may just be bad fuel or water in the fuel. I have run 2 tanks of fuel through it since I bought it from 2 different stations that are busy name brand stations. The fuel filter was replaced 3 weeks ago at the start of these problems. I will drive it over the weekend and see what happens. I find what they are saying hard to believe. This truck runs like crap almost everytime I drive it And they fix it from a can of treatment. I am new to diesel engines so will see what happens.

 

[1chevy02]

I bet you have a loose connection to a injector. If it does it again then see what codes it throws. If it says #7 injector thats probably what the problem is. Go on dp and search for ice pick fix. Very common on lly's and also very easy to fix.

 

[dirttymaxx]

could be the lines on the filter housing getting soft and closing when you put your foot in it,i have had that happen a few times in the past 3 mts

 

[PhilsLB7]

If he is getting air in the fuel system somehow would it act this way?

 

[KarlLLY]

Update: So far so good I have put about 300 miles on it and it seems to be running fine. I still can not believe that just dumping a can of additive in the fuel tank was the fix.

 

[KarlLLY]

Update: now put about 2k miles on it and all is well.
Thanks to all