bad converter ??
 

after motor heats up and I gun the engine a little I hear a rattling noise sounds like it may be coming from the cat , wont do it when the motor is cold at start up , would a bad cat do that ?

Yes these things are notorious for rattling cats, when the steel body of the converter heats up it expands and allows the catalyst (Honeycomb) elements inside to have extra room and they rattle, only real fix is to replace it, but.... i have seen guys drill a couple small holes and put a couple screws up into them and it shuts the rattle up for a while but it wont last forever.
On a side note, i replaced my "rattler" with a universal fit type that i ordered from partsgeek, it was $69.95 shipped to my door, i took my old converter in with some scrap metal and they gave me $70 for it. Im sure the $69.95 replacement isnt real high quality but i broke even minus 2 exhaust clamps. No more rattle, no check engine light and im not poisoning any magical unicorns.

replaced cat
 

cat was bad , so I had both cats and muffler replaced with Magnaflow parts ,, sounds nice not loud and runs a little bit nicer

I have a question. I have a 2005 blazer two door 4x4 and there is no magnaflow universal fit cat listed for mine, so my question is which one will fit? I ordered one online for 135 dollars taxes in and they said they wouldn't guarantee fitment? I canceled the order cause I was nervous. They did guarantee fit for a 350 dollar one and taxes on top of that. Any help would be appreciated.

Barry

Of you are doing the work yourself im pretty sure you can make it work, if its in the 2 to 2.5 inch inlet and outlet size then you can just go to a local parts store and buy reducer/adapter fittings and clamps to make it fit whatever size pipe you have, the key is to leave as much pipe on the vehicle as you can, cut just the cat out and no extra pipe if possible. I bought a universal fit unit from partsgeek for $70 shipped to my door. It worked but i sold the blazer soon after so i dont know how long it lasted, beware, cheap cats are just that...CHEAP. A scrap yard will give you 100 bucks for the factory one if the internals are still intact, they will only pay 5 bucks for aftermarket cats, that tells you something about the content and quality of these cheap aftermarket parts. I doubt they last anywhere close to 30,000 miles.

Yeh I am doing the work myself and will have to measure the pipe diameter. I'm hoping I can get a cat close to what I need minimizing the work. I was thinking the Magnaflow 51006 is the one I need. What do you think?

Well the fitment sheet on that one only lists 2wd blazers, not sure why, it may still work? Your best bet is to take a tape measure out and crawl under yours, measure the main bodys length, width and thickness and look to see if there are any clearance issues in case the new one is slightly wider or longer. If your measurements are pretty close to the spec sheet on this one then you should be fine. If you dont have calipers to measure the pipe diameter heres a trick, get a peice of stiff wire like a coat hanger, bend it into a U shape and form it so the points just pass over the outside of the pipe barely touching and then measure between the two tips of the wire, if its pretty close to 2.5 inches or just under then that means your stock pipe is 2.5 O.D. and this cat is 2.5 I.D. so it should slip right on. On my 99 2 door 4x4 the only thing that was close to interfering was a crossmember at the back but i managed to get a clamp up in there and make it work. Anyway i just rambled a bunch but hopefully some of it was useful, i think this cat will work for you....or you can MAKE it work. Good luck!

Thanks for that. Saturday is the day I look at it. Hopefully the snow will hold off for us. I will likely cut it off and then I will have a much better idea. I will only cutoff what I absolutely have to.