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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.
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