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2017 l5p Chevrolet 2500 LT CC
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Discussion Starter · #1 ·
This is my first post on this forum, but I have been a reader for a long time. The only reason that I have never posted before is that I don’t think I am qualified to post on most things. I would rather leave that to the people more knowledgeable than me. The contributors to this site have really helped me find the answers to many questions I have had about my duramax.

I am having an issue with my truck that I would really like some help with. I have searched and searched but cannot find any threads that address my issue. I have a 2013 lml that is stock besides a few “missing parts,” along with the tuning to support the missing parts. I towed with it a few days ago. It ran fine while I was towing. Later that day I started it back up to go somewhere else and heard a knock coming from the engine area. Only between 1000-1500 rpms. I could make it go away by accelerating or decelerating. If it started knocking and I kept the rpms steady it would continue steady, but only in that 1000-1500 rpm range. It is not throwing any codes.

The first thing I did was check the balance rates. Everything was within +/-.6 in park and within +/-1.5 in drive at operating temp. I went ahead and sent a message to the company that I purchased my tuning from. They suggested flashing to different ecu profiles to see if it follows. No matter which ecu profile I loaded the knock continued. Then I loaded the return to stock file. The knock was gone, but I was in limp mode. After that I was sure the knock was due to tuning.

Since then, I have driven more with the stock file. I think maybe I can hear the knock faintly. I am thinking that the tuning might not have anything to do with it, but the reduced engine power might be what’s making it go away. What could be wrong that the reduced engine power would have that big of an affect on?

Sorry for the long post, just trying to be thorough. I hope somebody takes the time to read this that can help me. Right now I am thinking possible injector going bad or exhaust leak. Would the reduced engine power make either one of those go away? I would think that I would definitely still hear an exhaust leak, but don’t really know.

Thank you in advance for any help.
 

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What type of a knock is it, loud metallic? Anyway you can get a video?

How recently was your oil changed?

No other issues, losing coolant, smoking, etc.?

If you’ve got a good scan tool, you could disable the injectors one by one and see if it changes anything and narrow it down to one cylinder. If you don’t have one available, just unplugging the injectors one by one will work too.

I would still get a good scan tool and see if it pulls up any codes. Just because the CEL didn’t illuminate doesn’t mean it’s not setting a code.


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2017 l5p Chevrolet 2500 LT CC
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Discussion Starter · #3 ·
I really wouldn’t call it metallic. I will try to post a video. Oil was changed 2000 miles ago. Not losing coolant. No smoke. I don’t have access scan tool. Using an ez lynk to monitor. I will call around to see if I can find a shop that can disable the injectors one at a time.
 

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2017 l5p Chevrolet 2500 LT CC
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Discussion Starter · #4 ·
Ok. I took a video and I think I was wrong. After recording the noise, it sounds pretty metallic in the video. For some reason my phone picked up the sound better than I can hear it sitting in the driver seat. I am fearing the worst with this. Thinking internal now. Rod bearing, broken crank, etc. I am trying to attach a video but it won’t let me. Do I have to have a certain number of posts before I can do that? Do I just attach a link to the video?
 

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Upload it to your WhoToob account, and then post the link to it.
 

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That's doesn't sound good, something bottom end wants to come out.
 

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2017 l5p Chevrolet 2500 LT CC
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Discussion Starter · #8 ·
Yeah, I agree. The video doesn’t sound good. Right now I am thinking your right, but why does it only sound like that in such a narrow rpm range? Also, why does the reduced power with limp mode make it go away almost completely?
 

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Sounds like a spun bearing to me, probably connecting rod. When it goes into reduced engine, the ECM turns off the injector on the cylinder that is knocking, and it goes away. Guessing you can figure out which cylinder it is by turning off injectors with a scan tool


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Discussion Starter · #10 ·
I like to do as much work on my vehicles as I can, but I am in way over my head with this one. I made an appointment with a diesel shop for a week from now. I will post what the diagnosis is when they figure it out.

I am getting ahead of myself here, but I would like some suggestions on anything that should be done if it is a bearing. Please tell me if any of this is wrong or just stupid. If it is a bearing, I assume the engine has to be pulled out to be torn down. Would the crank more than likely need turned or replaced? Is there any other mods that you would recommend while the engine is out? Cp3 conversion? I’m not looking forward to the price tag with a repair like this, but I’m not sure what other choice there is.

Thank you for the replies so far, this site really is a great resource.
 

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Discussion Starter · #11 ·
By the way this really sucks, I have an oil analysis kit sitting on my shelf waiting for my next oil change. I changed the fluids when I bought it 3 months ago and haven’t even made it 3000 miles.
 

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That sucks, how many miles are on the motor, was it a private sale or dealer?
 

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Discussion Starter · #13 ·
115000 miles. It was a dealer. I talked to the previous owner though. I felt really comfortable with the purchase but I guess you never know.
 

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I'd be taking it back to the dealer for some kind of warranty
 

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Discussion Starter · #15 ·
I bought it in a state where the dealers don’t have to provide a warranty. It was sold as is. I’m pretty sure I signed something that said I knew there was no warranty. I could have purchased an extended warranty, but since it was an ”older” vehicle it would have cost something like $2500 for one or maybe two years. That might not be the exact numbers, I’m just going from memory. I remember thinking it was outrageously priced, but its looking more affordable all the time. They did sell it to me already deleted, though. I’m sure they weren’t supposed to do that, if they ever even looked at it close enough to know.
 

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Discussion Starter · #17 ·
I said I would update this, so here it is. I took the truck to a diesel shop and left it for them. They have been driving it for two days and tell me that they have not been able to make it knock. I can’t hardly believe it, but I trust them. I sent them the video that I posted on this thread, just to prove I’m not crazy. If they continue to tell me that they can’t hear a knocking sound, I really don’t know what to do.
 

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I said I would update this, so here it is. I took the truck to a diesel shop and left it for them. They have been driving it for two days and tell me that they have not been able to make it knock. I can’t hardly believe it, but I trust them. I sent them the video that I posted on this thread, just to prove I’m not crazy. If they continue to tell me that they can’t hear a knocking sound, I really don’t know what to do.
That is really loud to me. If they can't replicate it, then maybe they can't replicate it. It never hurts to have a second shop look at it. It doesn't meant the shop you have it at now isn't doing a great job, but, if I heard that and had someone say they couldn't replicate it, I wouldn't be able to sleep. Wait for this shop to look at the video and try to find it, if they can't, I'd have another place take a look.
 

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Discussion Starter · #19 ·
The shop that I took it to came highly recommended by people I trust. It’s about 80 miles away, but I went there because they are supposed to be the best. I live in a pretty rural area so finding another shop to take it to that I would trust will be difficult.

They have had my truck for two weeks now and still have not been able to replicate the knock. After viewing my video, they believe it was a fuel knock. They think maybe I had an injector with a blockage holding it open and when I drove it down to them it cleared itself. Does anybody think that’s possible? It’s a good thing I took that video or I don’t think they would have believed me at all. I am going to go get it tomorrow. I will just have to drive it and see if it comes back.
 

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Could very well have been fuel knock. Let’s just hope it doesn’t come back.


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