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Old 10-31-2014, 10:31 PM   #1
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Advice needed on 2006 Duramax

I have found a 2006 GMC Duramax for sale. It has 135000 miles and is loaded. It was the personal tow vehicle of the owner of the local GMC dealership and is offered for sale at that dealership. During the test drive today I noticed a lot of black smoke under normal acceleration. I don't think this is normal and wonder if there is a problem I should be looking for. There also seemed to be a slight roughness when on the road. I couldn't pin it down but the truck just didn't seem to be a smooth as I thought it should be. I had just driven on the same road in my present F150 so I know it was not the road surface. When I first saw the truck it had a fairly decent set of Michelin tires on it, but was in the shop for tire replacement. When I returned later in the day to test drive the truck I found the Michelins had been removed and replaced with the original tires that have evidently been in storage for the past eight years, so that could be the cause of the roughness. The truck looks good, hasn't had any body damage, but I'm just worried about the roughness when driving and the smoke when accelerating. I sure would appreciate any advice from the members who are familiar with these trucks.

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Old 10-31-2014, 11:17 PM   #2
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Could be a sticking injector or a clogged air filter. The k&n type filters can cause that sometimes. Also it could have a bad mass air flow sensor. It should be scanned and if there is a mass air flow sensor code (they wont always trigger a check engine light) have them see if the ecm has a current flash. There was a flash that came out around '08ish that was a fix for some of the mass air codes.
Either way have them fix it before u buy it.
(Also some tunes or programmers will cause the engine to over fuel and blow smoke, I'd steer clear if it has been tuned, personally)
On tge roughness, besides the possibility of the tires, i would bet that the torsion keys may have been "cranked" or replaced to level the front of the truck. Doing such will add more pressure on the torsion bars and usually give a harsher ride.

Good luck!

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Old 10-31-2014, 11:42 PM   #3
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I drove this same year/model truck for 125K miles and it was great. The black smoke could be any number of things.... some bad, some not. You'd need to take it out and drive it for an extended time to see if it goes away. Mine would build up soot (for lack of a better explanation) and billow black smoke when I got on it for the first time in awhile. Generally, white smoke is much worse. The ride thing is tough to say and really depends on your baseline. Compared to an F150 the Duramax is going to ride A LOT rougher. There's just no way around it. It's a HD truck compared to a 1/2 ton which is designed for ride quality.

These are great truck and you have to pay top dollar when you find one that hasn't been abused and "modded" to the gills. I can't believe how much I got for mine when I sold it. This was about 6 months ago - 150K, totally stock 2500 CC SB 4X4 and I got $22K out of it.
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Old 11-01-2014, 06:39 AM   #4
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There is a sticker on the back of the truck that says "Banks Power". I'm assuming this is a tuner of some type but there are no gauges, switches, controls or knobs other than the stock ones. Can the tuner have been removed? Should this be a warning to look out for? I do plan to have a mechanic check it out before I buy.

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Old 11-01-2014, 08:19 AM   #5
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Does it still have its muffler and cat?You can have a tune in it.beware. If they took it out and never tuned it back to stock your ecm.could be locked.And need to be reflashed.
If you look at the 8th digit of the Vin make sure it has a letter D.
Which is a Lbz motor.Much better motor.
Love Mine at the time.And 2500 gm rides a little rough 3/4 ton but put a load on it and smooths out alot.
My stock chevy would blow a little black smoke .
Check the fuel filter first .
Good luck
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Old 11-01-2014, 08:46 AM   #6
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IMO...keep truck shopping...look very hard for a true stock '06 Duramax...from the sounds of your concern, you might be buying more trouble than good

...and don't count on the Dealership giving you all the details on that truck!
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Old 11-01-2014, 09:52 AM   #7
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I'd vote for a program installed too.
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Old 11-01-2014, 10:22 AM   #8
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I'd also be very leery of 8 year old tires. Tires are supposed to be replaced when they wear down to the indicators or 7 years, whichever comes first. Hard to believe they actually hung on to the old tires for 8 years.
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Old 11-02-2014, 10:34 PM   #9
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Originally Posted by kb4srn View Post
I'm assuming this is a tuner of some type but there are no gauges, switches, controls or knobs other than the stock ones. Can the tuner have been removed?
Yes, they can be removed. Or it can be a Hypertech "style" tuner that plugs in to the port, delivers the tune, and unplugs. I use a mild Hypertech tune on my LBZ for better fuel economy and efficiency for towing. The extreme tunes (100+ additional HP) are what you have to look out for.
If I were you, I'd have the truck checked out by a diesel pro. 135k on a LBZ should be nothing.
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Old 11-02-2014, 10:47 PM   #10
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walk away and keep on looking. Listen to your gut on this one.

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