04 Disco II. 258,000 miles. Engines been rebuilt. New wires, plugs, coils. Newer O2 sensors on front not back. Still running rough on idle. Throwing misfire codes 0304 etc. Only thing on my Disco that hasnt been replaced. Put new smog pump on, sound is deeper in base on start up almost like its forcing air to cats. Any help appreciated. Drove 156 miles on hwy to home, cel never popped on.

 

Check your fuel purge valve , if it’s sticking open it’s dumping vapours into your intake and making it run really rough and exhaust will smell

I had that issue

 

No matter, generic high-flow cats are beautiful enhancements to your Disco!

 

I was just starting to look at doing the cats and some new pipe. Looks like someone welded in some LR cats at some point. Sounds like it is not too difficult and the generic are good options - good to hear!