Have a 99 2500 4x4 LBCC. 97K miles 5 speed. Week ago started acting like water in fuel. running rough at idle. Checked fuel filter, etc., no water. Smoothed out at speed (1500-2000 rpm). Drove down town (3miles), stopped at stop sign, took off under normal acceleration, started loud knocking like someone under hood with sledge hammer. Shut it down as quickly as I could. Towed it to a local shop. Handle gas only. They started it and said it sounded like a rod knocking. Dodge dealer in SV said I'd have to bring it in. Have not checked with anyone else yet. So it's sitting in my yard right now.
Oil Ok. No rod through block. Tried code read through odometer-on,off,on,off,on----nothing but odometer reading. Suggestions?

 

that happened to my Mack truck. Does it sound like a bunch of pots and pans clanging together?
That's what his 500 Mack sounded like, and it was a connecting rod that broke.
I hope it's not that.

 

Worse than pots and pans. More like sledge hammer on block...or harley without pipes.
NRA Lifemember & former instructor

 

I'd say connecting rod.
Let us know when you find out.

 

The key on off trick only works on 00 and up. Some 99's can do it but a majority of them cannot.

If you know your way around and engine, I say pull off the valve cover and see if you see anything amiss.

My engine made terrible noises when a pivot stud on a rocker arm came apart and kicked over the Y bridge that pushes the exhaust valves on #5. Made a very nice series of knocking and rough running. Almost sounded like a .50 cal going off under the hood.