Hello all. My father's 2004 3500 is knocking like an angry neighbor when the music is too loud.
Some background; 2004.5 3500, 6 speed, 2wd, 190K miles. He bought it a while back with a cracked head. We did the head and all gaskets. A few thousand miles later the thermostat failed while pulling his fifth wheel and he overheated. We sent the head out again and new gaskets. Also installed Don's F1 (50hp) injectors. The block and pistons all looked great, and no issues when it was back together.
Several thousand miles later this happens; He came home from a very short, very mild weekend trip pulling his 5th wheel. Parked it in the driveway over night. Started it in the morning and the thing is knocking hard. This is not an injector tick, it sounds like a rod bearing. Check for codes by using key method and nothing. I started it and unplugged one injector connector at a time (the plugs on the outside of the valve cover that control two injectors each). RPM's dropped but stayed steady for the 1-2 plug and the 3-4 plug, but when I unplugged the 5-6 plug the truck stalled immediately. This test took a matter of a couple of minutes tops. After it stalled I noticed oil seeping from the lower exhaust manifold flange.
My first guess was valve seat, but with oil that far up, maybe hole in piston? The oil pressure gauge doesn't drop below the half-way center line, which is where it has always been while idling. There is also no noticeable smoke, although I have not given it any throttle. There does not seem to be signs of blow-by from the dipstick tube or coolant reservior.
Throw your bets in now. I will be tearing it down next week.
Thanks everybody.

 

Sounds like an exhaust seat has fallen out. They will do what was described. Run great and then shut off. Crank it back up later after it cools and the wonderful knocking. Don't run it anymore you may cause more damage. Pull it apart.


Oh, by the way. The oil pressure gauge is an idiot light. It is pre programmed to read whatever. It only detects low oil pressure below 6psi.

 

I wouldn't be shocked if it was an injector stuck open...

Are you sure its oil and not soot soaked fuel?

Oil pressure gauge is fake so don't put any stock in its reading.

 

If you lucky an injector is hung open or cracked on the pintle. If not, a valve seat likely has dropped. Pull the VC and check the piston height will give you and idea on that then a compression test will tell you if the cylinder(s) are damaged.