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Discussion Starter · #1 ·
New here and need some help.
I have a 2005 silverado with 130K miles on it. It's a stock truck with no tuner. I haven't changed anything on the truck.

Here's my problem.
When the truck is cold it does fine. When it warms up is when it notice the problem. When maintaining my speed at around 40 to 50 mph, it will start a loud knocking sound. Not the usual diesel sound but a louder sound like a rod is coming loose or something. Then the truck will start studdering (don't know a better way to explain this). It does it enough that people riding with me will notice it. It feels like the engine is shutting off and then back on real quick but I don't notice the RPM's changing so this is just what it feels like. It's usually around 1500 rpms when I notice it. If I'm on the interstate running about 70 mph it runs like a champ. Get off the interstate on the side roads coming home and it happens. Also, when I start out, if it's going to do it, it will knock briefly when I start accelerating from a stop.
I took it to the dealership and they said there was a service flyer out that said it needed to be reprogrammed. I had that done and it continued. I carried it back and had the service manager ride with me one day after lunch when it was doing it. It happened several times on may way to the dealership so I left the truck running so nothing would change. We took it for a ride and it took about 15 to 20 min of driving before it did it for the service manager. He said it felt like bad fuel and gave me an additive for the remaining fuel in my tank. I ran the 1/2 tank out that was left and it did it several times. I've refueled at a different station and it's still doing it. Truck idles fine with no unusual sounds and no smoke of any color. I have a fried with the same truck that has the same problem. Anybody else have this problem. I really like this truck but I don't know if I can trust it or not.

2005 Silverado 4x4
Stock everything
 

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My pickup does this exact same thing. Ever since i got the pickup at 100k it would have a slight surge with no knock at 1500 rpm's. it has steadily gotten worse. Truck now has 142k on it and at about 1500 rpm cruising it will just start knocking loud as hell and surge and be gone in a matter of a sec. I notice that if i stop at stop light and sit for a sec then go again it will sometimes do it much worse, but always at 1500. I don't think it has anything to do with torq converter. It is a bad knock like injector firing way out of time. I get no codes. Going to get a scanner on it tommorow and check fuel pressures and run some tests. I'm a diesel tech myself and very familiar with diesels but new to the duramax, I know this is not the normal ping that other people talk about. Any ideas would be apreciated.
 

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DIESEL MANIAC!!!
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isn't this the typical lly clatter? my lly did this from almost new
 

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I don't think so this is more like complete loss of power speed will drop ten miles an hour and about chirping the tires when it comes back. Sounds like a rod coming through the block and will actually almost shake the pickup because it comes so far out of balance.
 

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Anybody else have this problem.
I logged a truck (LLY) last week that had sudden anomolous behavior like described here. His is definately electrical, almost all sensor readings would burp simultaneously. I will prob replace the ECM, which is where I suspect his issue is.

fyi, when this happens, his timing would spike to 20 BTDC, and make for loud knock.
 

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This vehicle probably had codes didn't it? I will look for that today thanks for info
 

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Mine does the same thing but it starts at a high idle the drops down low and is rough. I noticed it at 1500/1700 rpms. It gets better as th truck gets up to 180* but is really load when under 180*. I'm going to replace the injector wirin for 1 and 7 and see how that works out. I also have a lift pump that is mounted but not wired. I will do that after and see if there is any difference.
 

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Discussion Starter · #10 ·
it's fixed

ok guys, heres what fixed it. After the dealer told me there was nothing they could do because there were no codes so they didn't know what to replace, I wouldn't take no for an answer. The service manager took me to a tech that worked there that had a duramax truck. He told me of a problem he had and we went to my truck. He opened the hood and went to the injector wires where they are wire tied to the support piece on the alternator. He unzipped the wire tie and lifted the wires up. They are in a plastic protective wrap. As he moved the wires to look at the bottom of them, you could see the bare wires through the wrap and insulation. He couldn't promise that would fix it so we left the wires off the alternator and I've had no more problems. Hope this helps you guys.
 

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These wires rubbing and wearing through seems to be an issue that causes many different symptoms. It has been talked about a lot in my research of this forum. Mine wasn’t worn through (yet) but I took a piece of heater hose and tie strapped it the wiring harness just in case, it also sits there lose, not attached to the alternator plate.

What do they say, Always start with the cheapest fix, that’s what I’ve learnt since joining the DF.
 

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I have the Exact same problem with my 2005 LLY...I have given my mechanic the link to this page and a few others for him to read...My injectors appear to run like a charm...most of the time but every so often, I have the "problem" happening...so it looks like we will start with inspection of the main wire to the alternator and see how that goes...then ice pick on all the injectors if necessary. With nearly 300,000km (187,000 mi), I have yet to change an injector, it works like a charm (knock on wood) nor have I ever put fuel additives/cleaner but I think its time to put in a high quality injector cleaner (stanadyne..milliganbiofuels, etc?) and fuel additive to see what happens. I will report after I do those things...appointment for November 10th, 2014!
 

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Discussion Starter · #13 ·
No need for an appointment to see if it's the same thing. Raise your hood and on top of the altenator, there will be a group of wires in a protective plastic cover. These will be tied to the alternator with a wire tie. Cut the wire tie and lift the group of cables ip. If it's the same problem, there will be an area of the protective cove that is warn away from the vibration of the altenator and you can see exposed wires inside it. Hope this helps.
 

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No need for an appointment to see if it's the same thing. Raise your hood and on top of the altenator, there will be a group of wires in a protective plastic cover. These will be tied to the alternator with a wire tie. Cut the wire tie and lift the group of cables ip. If it's the same problem, there will be an area of the protective cove that is warn away from the vibration of the altenator and you can see exposed wires inside it. Hope this helps.
Thank you...then I'll do this in the driveway this weekend. Interesting thing is that I had the alternator changed 2 winters ago...so I'm thinking it may have happened then?

On another note, I was going to buy some Stanadyne today but the dealer only had the performance stuff, not the cleaner. Then in talking to someone, they told me to go with Power Service instead....that it was a step up from Stanadyne... thoughts? clearly a few threads here.

Thanks guys, amazing support and wealth of information...in the end, I just dont want to get rid of my truck, it works awesome otherwise with proper preventative maintenance, it looks good and takes me to my best hunting and fishing spots year after year north of 60!
 

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I had the knock too. Ordered a gallon of Optilube XPD and added 16oz at fill up. They said it may take 3-4 tanks to notice a difference. I noticed it quieter in only 200 miles. Now after another 200 miles I can't hardly make it knock anymore. It's not cheap stuff, but it works!


Sent from AutoGuide.com Free App
 

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Well here's the scoop...the knocking was starting a few minutes after the truck started ...so it the engine had to be warmed for about 3-5 minutes then the knock would start and get progressively louder...it had nothing to do with truck speed, all about the engine speed. I took the chevy dealer duramax mechanic out with me, very nice and not cocky one bit...after listening to it for couple of miles, he was pretty confident, although not fully certain, that it was an injector knock and suggested he put the scanner to it to determined which injector was fouling. They took it in a couple days later and next thing you know, I had a $390 bill (I was very happy about that). As it turned out, he inspected the harness to all the injectors and sure enough, the #8 harness had a split into one of its wires rubbing on a sharp edge...he fixed the sharp edge then fixed the wire and now its running like a charm again! With 300,000km (186,000 miles), I had NEVER ran any additives in the truck but after doing quite a bit of reading here and other places on the web, I've opted to go with Power Service additive (bang for the buck...some claim to be better but also a lot pricier). Hopefully it will keep the injectors running for much longer!

So here's the end to my mystery, hope it helps anyone else who may run into similar situation. Putting on the ARB front bumper this week. Bolted on the rear Trail Ready already, it was easy and looks really sharp. Next the K-source towing mirrors and the bottom 6" all around in box liner. Oh yeah, still need to figure out which cold air intake to put on.. S&B Has a kit including cold air and larger mouth piece...may go for that.

Cheers!
 

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Knocking sound and spudders

Had same problem wire harness strapped to alternator rubbed raw some wires. Thanks to other post. Was able to fix while down in baja and got home safe. Thought I would share a photo.
 

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Knocking sound and spudders

Had same problem wire harness strapped to alternator rubbed raw some wires. Thanks to other post. Was able to fix while down in baja and got home safe. Thought I would share a photo.
 

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I have a 2013 with a lot of the same problems. Sounds like a rod knocking between 1200 and 1700 RPM. And only does it under a load. When the truck is in park it idles fine with no noise. I will look at the wiring when I get home. Any other advice would be appreciated.
 
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