Hey guys, I need new cats, was looking on Amazon, eBay, and rockauto. Anybody have any experience with cats from any of these? I found a 2 piece design knock off magna flow design looks pretty interesting. I don’t want to pay the magna flow price. Any suggestions or advice?

 

How did you diagnose that your truck needs new cats?

 

Well first thing was one bank was misfiring along with random multiple misfire on that bank 1,3,5,7. Then I did an exhaust back pressure test.

 

I've always used the cheapest ones I could find on ebay. Usually around $85 for two. Cut the old ones out and weld the new ones in.

 

While you may need cats, you should also do an intake smoke test. I had a similar issue on my old DII and it was bad injector O rings, so you could have a vacuum leak somewhere.

 

I had a set of magnaflows that both started rattling. The elements inside came loose. Dont use those.

 

What were the results of the exhaust gas back pressure test?

Did you have no codes typically associated with cats not working adequately -- P0420 and P0430?

Misfires all on one bank are more typically traceable to a bad upstream O2 sensor on that side or to an exhaust leak, although vacuum leaks affecting all four cylinders on only one side would be uncommon.

Have you tried changing the upstream O2 sensor, or swapping the upstream sensors side-to-side to see if the problems move to the other side?

 

All O2 sensors have been replaced. Compression on all cylinders is around 180-185psi so there no bad head gaskets or such.

 

Can someone describe to me the sound of bad cats? I have a weird exhaust noise that is worse at start up than after fully warmed up. Its not the motor but I can't quite put my hand on it. Thanks!

 

It could be the gasket between the exhaust manifold and the downpipe. That was the case with my truck. Upon acceleration, especially when cold, it sounded like a diesel.

I'm no expert in this, but from what I understand bad cats have a rattle. I'm sure others with more experience will weigh in.