Hey guys I was driving my 2002 chev duramax 6.6L, I was sitting at a light and I heard a little knocking noise. Didn't think anything of it take off from the light look in my mirror and the truck is blowing so black I cant see the car behind me !!!! Pulled into my shop 1/2" sec a way and it was banging and knocking and blowing so black it was crazy. Any ideas on what this can be ???

I am hopeing for injectors??\
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Sounds like overfueling - do you have a pyro?

Maybe a injector stuck open? Definitely over fueling!

Mine is doing the same thing. Bad loss of low end and I am in Santa fe needing to get home with 9000 lbs worth of TT. It drives fine once I get up to speed but it isn't doing so well getting up from a start. Mine started when I came down off of Wolf Creek pass and was using the grade brake. I got to the bottom of the mountain and stopped for a minute and all of a sudden it started in. It has diminished quite a bit in the last 4 days but it comes and goes a lot. Any input, I hate to go down for injectors on vacation on my last leg home.
BTW, it only seems to overfuel and smoke when I have to get on it to get moving. Other than that it seems to run okay. But there also seems to be loss of power now that I think about it because the truck was having trouble keeping speed on hills that it never had trouble with before.
Thanks:(

Mine is doing the same thing. Bad loss of low end and I am in Santa fe needing to get home with 9000 lbs worth of TT. It drives fine once I get up to speed but it isn't doing so well getting up from a start. Mine started when I came down off of Wolf Creek pass and was using the grade brake. I got to the bottom of the mountain and stopped for a minute and all of a sudden it started in. It has diminished quite a bit in the last 4 days but it comes and goes a lot. Any input, I hate to go down for injectors on vacation on my last leg home.
BTW, it only seems to overfuel and smoke when I have to get on it to get moving. Other than that it seems to run okay. But there also seems to be loss of power now that I think about it because the truck was having trouble keeping speed on hills that it never had trouble with before.
Thanks:(

The Dmax does smoke a lot more at altitude. Last year on vacation in rockies (west of Denver) I could make the truck smoke tons at will. Mine has always knocked louder than others, so I can't tell you about the rattle.

38,000 miles with fingers crossed (and toes!)

I am kinda thinking now that mine was a combination of altitude and extremely dirty air filter causing a lack of air to the engine. That might explain the loss of take off and smoke but still doesn't explain the knock, unless you can attribute that to low oxygen levels as well.

The truck ran progressively better the lower in altitude I got and the knock went away after a day in Santa Fe. The only thing that I did (and I don't know that this did anything at all) was de-tune the truck let it run for about 30 minutes then put the 80 hp program back on. I didn't notice an immediate difference so I sure as heck don't know what happened but am glad it was running good again. Heck I even got about 11.6 mpg from Amarillo to Ft Worth at 70mph running mostly into a slight headwind.

Who knows?:confuzeld

Ok, to update this thread. I spoke to a friend of the family, who is a GM Tech and described to him what was going on with the knock and smoking. He said it was definitely overfueling and it was more than likely because the MAP sensor and other air/oxygen sensors were not able to calibrate or re-calibrate themselves for changes in barometric pressure, ie changes in altitude.
He said that normally the truck should "learn" as you are driving and automatically adjust but he did say that with a tuner or chip that the adjusted program would probably not allow the PCM to adjust as much as it needs to.
The knock is caused by way too much fuel and not enough oxygen. That was also why my truck was running over 20psi boost climbing the mountains while it was trying to adjust for the lack of oxygen.
After I detuned and let the truck "relearn" for 30 minutes, it fixed itself and then allowed me to be able to retune the truck.
He advised that if you are towing in altitude or going to be changing altitude rapidly to remove the tune every few thousand feet altitude change and let the truck run stock for a about 15 minutes to adjust to the change. If it is not possible then do that at the first possible time. And make sure the air filter is clean (which mine was not) because it didn't help that I was starving the truck for air.
That was the explanation given to me and made perfect sense for what was happening to me. I'm sure that there are a few variations of the basic principle that could be causing a lot of the overfueling conditions that people are getting.
My two cents.