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Discussion Starter #1
I bought the 07 in December and it would always start right up and run smooth. The last few starts the truck shakes and knocks after starting and even while driving around you can hear the knock. I was starting it in cold weather before no problem. It sounds bad on a 60 degree day now. After driving for about 20 to 30 minutes the sound goes away and the truck sounds perfect. Also if I put my foot into it the sound will go away but as soon as I let of the throttle and run at a set speed the knock comes back. Sounds really bad when taking off from a stop. What could this be??? I took it to the dealer and they said that if no warning lamps are coming on then it is probably a cold motor. I took it out today and it was running 195 degrees and was still making the sound. Drove the truck around at all different speeds and RPMS and the nosie stayed there until 30 minutes later after going 60 mph I let off and the sound was gone. The truck has 2000 miles and I have really been impressed with the truck up to this point. Did not pull with the truck until it had over 1000 miles and before that I never ran at one set speed or rpm. I let the truck warm up three to four minutes and cool down before shutting off. So what could this be? I have run diesels my whole life and have never heard this before. Thanks for any help. Alan
 

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"I took it to the dealer and they said that if no warning lamps are coming on then it is probably a cold motor"

Did the dealer check for any codes? If not, find another dealer.
 

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Find a new dealer. Also, have them check the balance rates.
 

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Hey Alan,

I just got home from work and "lucky" me....I too now have the same exact symptoms!! I also have 2000 miles and have never had a problem until today. Knocking loud just around 1500 RPM. Also, have no check engine light. Let me know how you made out. I'm going to try and bring it to the dealer tomorrow. Anyone out there have any other suggestions?? Thanks:rolleyes:

P.S. Warm engine drove around for about 20 minutes in 40 deg. weather....what gives??
 

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might be an injector issue, find a dealer you can trust and let them look in to it
 

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Im sorry cant help w/your problem , but my dealer is the same. I pull in after work few times at the dealer tell the tech to come over. in the shop park, floor it, truck revvs right up to 2100 rpm holds at 2100 rpm for about 5-7 seconds (what it does when driving it) stays there and then takes off. Can hear the turbo whistle so I dont think its because its sppoling up (and 7 seconds is a heckc of a long time), but the dealer says"theres no check engine light" the dmax is highly sensitive tons of sensors if anything is wrong youll get a light" Those were the exact words he told me one day. I know its somethign to do w/my problems of low rail pressure (the thing having a dead spot) but some dealers knowledge on these trucks stink.
 

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jiggs420;1625007; said:
might be an injector issue, find a dealer you can trust and let them look in to it

i was going to say the same thing my fathers 01 duramax did the same thing, it made like a very slight ticking or knocking noise but loud enought to notice it was different, and it was the injectors never set the service engine light off or a code, he had the dealer check it like 5 different times finaly they had a mechanic drive around with my father with a there programer so he could show them what he is talking about, the way they found out was when the mechanic added more fuel to his truck the noise went away thats how they found out it was a injector prob
 

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Discussion Starter #8
Went to the dealer a second time and they checked and there were no codes, and said that everything checked out okay and then went ahead and told me that GM calls this normal. Well that's just fine and dandy but two days later I start the truck and let it warm up for a few minutes and drive through town on my way to the freeway. Every stop I make I hear that d?*n knocking noise! I get on the freeway and am doing 75 for 10 minutes and the truck is running smooth and sounds good, when all of the sudden the truck starts to shutter and knock like no other. I was blowing white and blue smoke out the back to the point that I could not see anything in the three lanes behind me. I let off the throttle and it went away. Put my foot back on it and then it does it again. It is now doing this off and on all of the time, and I yet to see a light come on in the dash!! Taking it back into dealer in a few days to see what now but I am sure that they will find nothing wrong again for the third time. Really impressive to pay over 40k for a truck that you can't drive around town and listen to the radio or talk to your wife without hearing knocking and ticking coming from the engine. Everyone is saying how they like the sound because it lets them know they have a diesel! I bought for power and performance, not sound!! To bad sound is the only thing they have delivered on yet!!!
 

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Also think this sounds like injector issue, i would also pull the filter and check for bad fuel, you can get lousy fuel at any time. Have found all kinds of trash in diesel in the past, even right after new filter was installed, also did you accidently put gas in?
 

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akw321;1629341; said:
GM calls this normal.
Dealer BS, it's not normal. Get a friend to ride behind and take a picture of the smoke, send the picture to the dealer and a copy of it to GM and ask them if it's normal.

After sending the picture, wait a day or two and then call the dealer and ask again if he can repair it, if can't contact GM customer relations and ask them why it can't be fixed.
 

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did the dealer atleast check the balance rates on the injectors? with the issue you are having i think thats the first thing i would do.
 

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Discussion Starter #12
I also think that it is an injector issue and am hoping to have a come to Jesus talk with the dealer on Tuesday. Am I going to have to sit there and tell the dealer to do these test or will they know to check for these things? I am going to have them change the fuel filter and check the injectors. You guys seem to know more than the dealers so thanks for your input and help. I really like this truck when it comes to comfort and the transmission, but that damn Duramax is yet to impress me. Good power and runs nice traveling higher speeds, but just to inconsistant on performance. More tempermental than the wife!! Anything else you think I need to say to the dealer let me know, and thanks again. Alan
 

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akw321;1629784; said:
I also think that it is an injector issue and am hoping to have a come to Jesus talk with the dealer on Tuesday. Am I going to have to sit there and tell the dealer to do these test or will they know to check for these things? I am going to have them change the fuel filter and check the injectors. You guys seem to know more than the dealers so thanks for your input and help. I really like this truck when it comes to comfort and the transmission, but that damn Duramax is yet to impress me. Good power and runs nice traveling higher speeds, but just to inconsistant on performance. More tempermental than the wife!! Anything else you think I need to say to the dealer let me know, and thanks again. Alan
Sorry your having bad luck with the Duramax. I would say 95% of the people is sastisfied with the whole configuration. Overall its a good truck...No problems from mine yet...
 

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Hey Alan,
Dropped my truck off at the dealer today. I'll let you know what happens. On the way there, truck was shuddering/knocking and smoking like crazy. Couldn't go over 55 mph. Pulled over for 3 minutes. Started back up and was a tiny bit better, but still not right. Let's hope the dealer finds "something" they can fix since I still didn't get any check engine light!!

P.S. Changed filter today and truck actually runs worse now:eek:
 

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akw321;1629784; said:
I also think that it is an injector issue and am hoping to have a come to Jesus talk with the dealer on Tuesday. Am I going to have to sit there and tell the dealer to do these test or will they know to check for these things? I am going to have them change the fuel filter and check the injectors. You guys seem to know more than the dealers so thanks for your input and help. I really like this truck when it comes to comfort and the transmission, but that damn Duramax is yet to impress me. Good power and runs nice traveling higher speeds, but just to inconsistant on performance. More tempermental than the wife!! Anything else you think I need to say to the dealer let me know, and thanks again. Alan
PM RickDLance about the dealership with your experiences so that everyone else knows about it.

Ask them if they have a diesel tech. If they don't, go to another town. You might have to tell them to check the balance rates, you never know about some dealers.
 

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All you need is a blocker plate and finger stick ........ Your EGR valve is stuck open allowing to much exhaust fumes in ............. it will run very rough, do a Search on ( Blocker Plate ) ;)
 

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Discussion Starter #17
LS6Caddy;1633045; said:
Hey Alan,
Dropped my truck off at the dealer today. I'll let you know what happens. On the way there, truck was shuddering/knocking and smoking like crazy. Couldn't go over 55 mph. Pulled over for 3 minutes. Started back up and was a tiny bit better, but still not right. Let's hope the dealer finds "something" they can fix since I still didn't get any check engine light!!

P.S. Changed filter today and truck actually runs worse now:eek:

Hope that they can figure it out for you. Let me know what they say! I am taking my truck in first thing in the morning to see if they can do something for it. My dealer is Harmons in Provo Utah. I hope that they can fix this because there reputation is on the line. The problem with alot of these GMC dealers is they often sell a couple of different cars lines and they seem to be top priority. Cadillac, Pontiac for example. I will let you guys know tomorrow what we find out. Alan
 

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Alan,
Balance test can back and now I need a new set of injectors!! Dealer said it might take a few days to get the parts in. They're hoping to get the truck back to me by Thursday. I'll keep you posted. How is your truck running these days? Mine really got worse day after day:mad: It started to run really rough, knock even louder, and smoke constantly. Let's hope this is the FIX.

Tim
 

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Discussion Starter #19
LS6Caddy;1635208; said:
Alan,
Balance test can back and now I need a new set of injectors!! Dealer said it might take a few days to get the parts in. They're hoping to get the truck back to me by Thursday. I'll keep you posted. How is your truck running these days? Mine really got worse day after day:mad: It started to run really rough, knock even louder, and smoke constantly. Let's hope this is the FIX.

Tim
Tim,
I am scared to go drive the dang thing. When I first bought the truck you could'nt keep me out of it!! Now I am worried about what else is going to go wrong with it. Just the sight of it and I start to get pissed off. I am guessing that my truck is going to need the same thing as yours. When was your truck made? Month/Year? We should do some checking and see if they are close to each other. Probably made on a Monday or Friday!! Monday they didn't want to be there and Friday they could'nt wait to leave!:) I'll check back with you tomorrow and let you know what we found out. Hopefully I won't have to change dealers on this one. Alan
 

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Just came back from the dealer and guess what? Truck is still sitting in the same exact spot that it was on Monday. Spoke with dealer earlier and said of course they started working on it and I should have it by Friday afternoon!! They haven't even begun to work on it from the looks of it. Looks like I'm going to have to give GMC customer assistance a call! A whole week gone by and still nothing.
Alan, my build date was April of 2006. If I ever get my truck back, I'll let you know the exact date.

Tim
 
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