Pull codes!

 

You can get the codes pulled for free at most auto parts stores. Advance, O'Reillys, etc.

 

Suggestion:
Get the parts together - plan a long day in the garage...
new cat, plenum gaskek, new plugs- easier to change than clean. Then clear the codes and see if codes reapear and how vehicle performs (MPG).

Do NOT assume what the codes are.... not correcting a cel would keep you from knowing any NEW codes.

SWAG: the cat failed because of a fuel problem - likely the intermittant cel was the clue we need.

 

If the cat actually grenaded and wasn't just clogged, all the chunks could now be living in your muffler and blocking it up too. Would give the same effect on mileage as the cat being plugged.

 

It turns out it was just a completely ****ed front O2 sensor, it was causing the truck to run super rich thus fowling my plugs and giving me horrible milage

All is better now, thanks for the help guys

 

May still be a bad plenum. Along with the cat, a leaking plenum is also known to screw up your front O2 sensor.

 

The cat is removed now, it was completly ****ed, the reason the o2 sensor was ruined was because the guy who removed the cat welded the o2 sensor in for some reason (which I'm sure fried it)

 

Plenum..........

 

ALL these problems because you ignored the CEL?

PS I agree with Zman17 do the plenum AND I'll add do the cat.

 

welded in the sensor, or welded in the bung for the sensor ?
its normal to weld in the bung.
um, not normal to weld in the sensor itself.

its also normal that an 02 sensor fails after getting knocked around during cat surgery.