I've got an '04 Sierra with about 82,000 miles on it. It's got a CAI, muffler and a stupid little hand held tuner (got that before I came to this site!). The truck has recently developed a loud rattle/knock in the 1-2k rpm range. The noise changes with engine speed and sounds like it's deep in the middle of the truck. It's a consistent noise up and down through that rpm range and isn't to noticible at any other RPM.

I think its a bad thing, rod knock, or not so bad, loose Torque Converter Bolts. Anyone have this issue, or had this issue and resolved it?

 

Cut the oil filter open, and see if your rod brgs are there....
Use only a snips, or a filter cutter, to avoid chips from a saw, etc, contaminating the pleats.
Any change in oil pressure?As you mentioned, loose verter?
Loose balancer bolt?
Take off the belts, and start the engine. still there? That'll let you know it is/is not an accessory.

 

Catalytic converter probably. Easy check if it makes noise while idling hit cat with rubber hammer and if noise stops for a second that is your problem.

 

Pulled the Y pipe off today, lots of silver chunks and powdery lookin stuff came out of the drivers side pipe. Looks like the cat took a dump on me.... Anyone know how much a replacement with cats is, or how much work is involved to install an ORY? Would I need a tune to do that?

 

Just gut the cats, get a tune from Charlie Wheatley and have him turn off the rear o2 sensors.

The Y pipie from GM is $700 or so, or you could have a cat welded in.

OR you could put a nice set of headers and Y pipe on, either LPP, pacesetter or OBX for $500.

 

How much is a tune? I'm kinda tryin to be low budget, I was thinking about just cutting the cats and welding some pipe in. We don't have emissions... so that not a problem

 

Wheatley is charging I believe $215 after you return your original pcm to him (It's like $275 I wanna say full charge?) It's reasonable considering you get free retunes for life. I'm milking him for all he's worth on retunes, lol.

 

Your welcome.

 

Thanks! That is the weirdest damn thing! I first went under the truck I swore it was comming from the trans pan... then my dad listened, he was brave enough to put his ear damn near on the CAT/Y pipe and figured it out.

What did you do to fix yours?

 

Cat overtemp? Usually what we see w/ a problem like that.
[Other than "gee, I didn't think I hit the ditch that hard", excuse]