Changed out the cat. converter on my '98 SS/T, and..

[hemi68charger]

Found this system on performancepeddler.com, good deal, $185 shipped.. Well, I installed it without any major hiccups, I did smash the tip of the upstream O2 sensor on the way out, but it didn't "seem" to compromise it.. That later... Anywho, I got it installed and now she runs REAL rough like she's going to stall at idle. Maybe the original O2 sensors are gone? The original cat. converter has been rattling with guts all broken inside, but never had an engine code indication and running like it wants to stall....
Will bad O2 sensors cause a '98 fuel injected 5.9 (360) to run real rough?



1. Original system. The original pipes are in excellent shape. Might as well keep it for future use..



2. Sitting in there now, the cat.. Has a definite throatier sound now.. NO MORE RATTLING !!!



3. Rear pipe going into the original muffler... Fit pretty darn good



4. Looking at it from rear forward...

[BrianShaughnessy]

Not real sure on your problem...     go to autozone and get a code check if possible.

Otherwise... got a link to that system?   I can't seem to locate it.   Does it have  dual 2 1/4"  into 3" or stock sized 2 1/2"?

I did a home brew 3" exhaust on the 5.9 Limited.      3" in/out magnaflow cat,  magnaflow SS muff and 3" SS tailpipe.    Had a local shop bend up new 2 1/4" Y pipe and install it all for way too much money.   
This was after I put on 93 exhaust manifolds with the bigger outlets.    I had put on a new rear O2 to fix a CEL  and gave the exhaust guy a new front O2 to put on with the system.
The rear O2 is located on the rear of the cat on a Grand.
I have way too much invested into the exhaust of my Grand... but it sounds great 

[68 RT]

Yes, you should always install new o2 sensor(s) when changing cat(s). 

[hemi68charger]

Took her out on a test drive today to fill her up.. Idles great and if I'm not imagining it, she's running better than ever. New sensors and a tune-up...  

Oh yeah, no rattling from cat guts........... The best part...........