my cat rattles at low speed/rpms. ive heard that not all rattlin cats are bad, but i want to know for sure.

 

waht kinda mpg ya gettin...ull knowby that that is the easiest

 

mine does the same thing but around 2000 RPM and my gas mileage is fine its right around 16 sometimes a little lower depending on how i feel like driving that tank or the winter gas and other factors

 

well seeing how i got a 5.9L, i get about 9 around town. (sucks but thats wat u get for havin a kicka$$ r/t)

 

so if it ratlles and i hav average milage, duz it still need to be replace?

 

you should get atleast 12.... and the cat can be checked...hit it lightly with a dead blow and see if it sounds like a bunch of rocks in there if so replace it...

 

lol.. thats not normal. 12city - 17highway is normal.. for a stock 5.9

i have a some stuff done to mine and i dont even get 9mpg. I get about 14 avg.

You should check your o2s also. having bad o2s can also f-up your cat. You should have ine right before the cat and one right after, very easy to take off anc check..

Also if you replace the cat, a highflow cat is good, but somtimes you may have to replace the sensors with a aftermarket brand, due to the factory sensors only working under factory cats flows.

or you can also get a o2 SIMM Fastman sells them, you buy one and it replaces your rear o2 sensor with a computer that tells your pcu you have a perfect flowing cat.

 

make sure it's not the exaust banging against the frame,
I had this problem when i got the truck, One of the front hangers broke and at low speed accel. it banged around and sounded like sh*t

 

yeh today i brought it into my auto class. i hit it and it sounded like loose debris inside. i also checked the temp on both ends. it was a lot warmer on th inlet side than th outlet side. so it seems as tho im gonna need to replace it.thanks

 

yea, be carefully not to breathe the **** that falls out of it...whear a mask or something, well this is what Ive been told...