Bought a Truck and a story - Chevy and GMC Duramax Diesel Forum
01-04.5 LB7 Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

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post #1 of 9 (permalink) Old 11-30-2019, 09:14 PM Thread Starter
 
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Bought a Truck and a story

I bought a 2004 Siverado 2500 HD with a LB7 with 264k on the odometer. The truck had been parked for 5 years and was in a no start situation. I was told that the injectors had just been changed (rebuilt)and that it was running great and all of a sudden he had a fuel delivery issue. He thought it was the filter head and he replaced it and could never get it to primer after, there it sat for 5 years. So I bought it...for better or worse. I decided that I didnt want to chance using the old fuel and have done all my testing with a funnel connected to the fuel line running to the cp3. today we were all set to do a fuel return measurement test, as last Saturday we couldn't get it to run off the funnel. got all set for a 15 second crank test and low and below it started... has a loud knock but it started. I took a couple of videos of it running and I am hoping to get your thoughts. I am new to diesel and I am learning as I go...
Link to the videos:
https://photos.app.goo.gl/A5jukr3X1WP5CEB37
The first one (29 seconds long) is interesting as you can hear the sound start before the engine starts and after it has turned over a couple times. The video that is 41 seconds long shows the exhaust.
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post #2 of 9 (permalink) Old 11-30-2019, 11:15 PM
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That is loud!

Ouch!!!

Welcome to the Forum!

Please take a moment to fill out your signature line so everyone will know the basics on your truck.

Search is your friend, here and on Google and these terms: loud knock lb7 duramax

...produced numerous hits, most pointing to injector issues. I believe it is usually caused by an injector stuck open, causing fuel to light off as the piston is rising. I don’t want to bad mouth the person you bought the truck from (OK, I will) and I wonder if he was telling the whole story. Fuel delivery problems immediately after injector R&R sound unusual, and as frustrating as that problem can be, it doesn’t take a rocket surgeon to diagnose the problem, which can be investigated without a running engine.

As you may know, fuel delivery is provided by a vacuum pump which is built into the CP3 (also, the high pressure pump) and any air leak between the CP3 and the tank will break that vacuum and, no fuel. The fuel filter head is of course the first place to check and the fuel delivery issue should be sorted before you go further. Bypassing the micron level filter by feeding diesel directly to the CP3 is risky, since any contamination you might introduce will make things worse. Lots of suggestions here on dealing with that situation, one of which involves slightly pressurizing the fuel tank at the filler and looking for diesel leaks.

Do you know if the injector work was by a shop or was it diy?

Surely a shop would have stood behind their work, but someone who just finished their own work (a lot of effort and expense ), may have thrown in the towel and parked it when their efforts were greeted with that loud knock and going back under the valve covers was not an appealing option.

Continuing on the knock problem, a shop with proper equipment can help you by disabling each injector in turn and when the offending unit is shut off, the sound will go away.

Get that fuel delivery situation fixed and go from there.

Stay in touch.
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2003 GMC Sierra 2500HD SLE ExtCab CA Emissions; 155k; Allison 1000 w/Transynd X2 Flush & Fill; 8' bed; AFE/CAI; MBRP 4" Exhaust; Side Tint, 33% VLT, rear, Limo; Smittybilt Stainless Side Nerf Bars; Sprayed-in Bed Liner; MadJack Fuel Filter Access Door; Regular Used Oil Analysis (latest available on request), Blackstone Labs; EGT/Boost Gauges; Dual Chrome Dipsticks, JC Whitney; Stainless Steel fuel filter head bleeder screw; New WP and Hydroboost; Billet Aluminum Fuel Filter Housing Spacer; Professionally repaired instrument cluster (new steppers and lamps); Does anybody ever read this s%#t?; Injectors under warranty @ 70k; 2nd set DIY @ 155k
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post #3 of 9 (permalink) Old 12-01-2019, 11:22 AM Thread Starter
 
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That is solid advice. It just wanted to hear it run and push some old fuel out of the return lines. I have already dropped and drained the tank, washed and dried the inside of the tank and inspected and cleaned the fuel pickup. I will get it put back together "correctly" and then had the diesel auto teacher at a local voc school run the described test. The Story with the truck was...he "had a guy" do it and he had another local shop with a good reputation rebuilt the injectors. Got it home had an issue with a torn boot on the air intake that caused a MAS issue. He googled his way out of that... then he says it drove great for a couple of weeks and developed this fuel delivery issue. He thought it was the fuel filter head and changed that out, when I started investigating I found the lines were reversed.... It was never going to prime that way. He had another truck, so there it sat. I think that he has just enough knowledge to dangerous...kind of like me. This is not my first rodeo, I have bought a number of boats, motorcycles and trucks in kind of situation before. This guy seems like a pretty straight shooter This being my first diesel, I didnt know all the questions to ask or red flags to look for. I am getting a pretty good education now.
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post #4 of 9 (permalink) Old 12-01-2019, 12:10 PM
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Thumbs up Back story!

Well, that clears a few things up .

A visit to a Bosch video site will show you the surgical cleanliness and attention necessary to properly work on injectors, and a “rebuild” by a “reputable shop”, no matter their care and experience, is unlikely to produce factory level injector performance.

Regarding swapped fuel lines, when I did my injectors I nearly went to the filter head with the lines, before the Fuel Injection Control Module (FICM) and caught the mistake after reference to a drawing. While that routing isn’t correct, I’m thinking it still should have primed, but whatever.

Sorry I beat up the PO. There’s an old saying, “Do not ascribe to malice, that which may be satisfactorily explained by mere ignorance.” That quote usually includes the word stupidity, but too harsh in this case. .

Still pondering the scary knock, but you seem to be a smart guy and I have no doubt you will make a correct diagnosis and have things sorted in due time. This Forum is a treasure house, and did I mention Search? .

I remain puzzled by your video of the tail pipe, since a loud knock generally presents with some manner of unusual exhaust emissions. Black, white, purple? Can’t recall. Yours is mysteriously clean, which makes me suspect a major mechanical failure, but let’s not go there till you get fueling figured out and do further diagnosis.

Stay in touch and be safe under the hood!

2003 GMC Sierra 2500HD SLE ExtCab CA Emissions; 155k; Allison 1000 w/Transynd X2 Flush & Fill; 8' bed; AFE/CAI; MBRP 4" Exhaust; Side Tint, 33% VLT, rear, Limo; Smittybilt Stainless Side Nerf Bars; Sprayed-in Bed Liner; MadJack Fuel Filter Access Door; Regular Used Oil Analysis (latest available on request), Blackstone Labs; EGT/Boost Gauges; Dual Chrome Dipsticks, JC Whitney; Stainless Steel fuel filter head bleeder screw; New WP and Hydroboost; Billet Aluminum Fuel Filter Housing Spacer; Professionally repaired instrument cluster (new steppers and lamps); Does anybody ever read this s%#t?; Injectors under warranty @ 70k; 2nd set DIY @ 155k
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post #5 of 9 (permalink) Old 12-01-2019, 02:14 PM
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Originally Posted by stevewaclo View Post
I remain puzzled by your video of the tail pipe, since a loud knock generally presents with some manner of unusual exhaust emissions. Black, white, purple? Can’t recall. Yours is mysteriously clean, which makes me suspect a major mechanical failure, but let’s not go there till you get fueling figured out and do further diagnosis.

Stay in touch and be safe under the hood!
I was curious of that also. I would think if an injector or injectors were that stuck to make that much racket that there should be a ton of smoke. What does it look like with the oil cap off while running?

2003 Silverado 155K. S&S stock SAC injectors, Kennedy dual lift with mega filter, aFe intake, the rest is bone stock.

Last edited by Hook'em_Horns!; 12-01-2019 at 02:48 PM.
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post #6 of 9 (permalink) Old 12-01-2019, 03:49 PM
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Hate to say it but, that thing has bigger issues than a fuel knock, that's a connecting rod wanting to come outside I couldn't even watch the entire 41 secs without getting a shiver lol

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post #7 of 9 (permalink) Old 12-01-2019, 07:43 PM
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Hate to say it but, that thing has bigger issues than a fuel knock, that's a connecting rod wanting to come outside I couldn't even watch the entire 41 secs without getting a shiver lol
When I watched I got a similar feeling. It sounds way too "solid" to be an injector(s). If it was me, I would be doing a compression test to see if you got a cylinder that reads way lower than the rest. I am not that familiar with these engines, but if I had to throw out a guess it would be one of your rods is bent, allowing that piston skirt to play kissy touchy with the crank. I hope you did not pay anymore than $1500 for her.

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post #8 of 9 (permalink) Old 12-01-2019, 09:13 PM
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Hate to say it but, that thing has bigger issues than a fuel knock, that's a connecting rod wanting to come outside I couldn't even watch the entire 41 secs without getting a shiver lol
Have to agree from the video and previous experience with a friend's LB7. I'll try to find the clips from his, it sounded JUST like this before it threw the rod heading down the freeway.

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post #9 of 9 (permalink) Old 12-07-2019, 10:08 AM
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I bet it had a fuel issue over fueled the cylinder and hydro locked the cylinder and caused major damage ..Just a guess tho . Hope its something simple for your sake . Good luck

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