Hey everyone, I’m a new member but have been lurking for years. Let me start off by saying this forum has been a big help over the years and I’m happy to finally be a member. I’ve got a 2003 ram 3500 4x4. I bought the truck sight unseen in June 2020 with electrical issues and a wounded 48re. I’ve since solved the electrical issues and converted the truck to an nv5600. The truck runs flawlessly but has a fairly loud bottom end sounding knock only under load from 1700ish to 2100ish rpm, only when you’re on the throttle under load. Its quiet until the oil gets up to temp. I’m a mechanic and have auto ingenuity if anyone is familiar with it so I’m able to perform injector kill tests. When number 4 cylinder(number 6 on auto number ingenuity for anyone that knows it’s quirks) is disabled the noise is completely gone. This led me to believe I had a simple injector problem on cyl 4. I replace that injector with a local parts house reman and then noise was still there. I pulled it back apart, ran the overhead, checked for bent pushrods, or anything else wrong in the top end, and also swapped injector number 4 and 1 with no change in sound. Everything in the top end looked great and the overhead was spot on. I continued to drive the truck for several thousand miles expecting it to get worse and it never did, so this weekend I tore into it. I removed the head and pan Saturday and removed the number 4 rod and piston fully expecting to see some kind of bearing issue or wrist pin issue but everything looked great. All of the cylinders still have great cross hatching at almost 190k and the engine had no blow by. The rod bearings show some wear and there was minimal wear on the mains also, nothing that would cause a knock. At this point I have no idea where the noise could be coming from and I hate to put it back together knocking it’s still going to knock. Sorry for the long post, any help, advice, or similar experiences would be greatly appreciated.

 

I think you have everyone stumped! If you kill the #4 injector and the sound goes away completely but returns with a new (reman) injector it almost sounds like a valve issue. (Just because of everything else you checked) With the head off did you check the springs on cyl 4? Or a valve recessed into the head enough to make the noise which could explain why the noise is gone with no injector pulse.

 

I haven’t had the head checked at a machine shop but it’s flat, no broken valve springs, no sunken valves, etc. I’m definitely stumped on this one, I’m just glad it’s mine and not a customers or I’d really have some explaining to do.

 

Any chance you checked#3 just curious if the running mate is the issue