Well, I think it is my cat but im not sure if it is the o2 or cat, Im pretty sure my cat rattles after being put to 3,000 rpm. When I rev the engine past that you start to hear this grinding type noise. But also at one point or another the check engine came on, for the front o2 so I am not sure. I am pretty sure I am just going to cut the cat off and put a pipe in place. But what should I do replace both or one? Right now the check engine light is off but last time I filled the tank full and drove i got 8mpg.

 

id replace the cat and the pre o2 sensor, pass emissions and better for the enviroment, plus ur legal!!!

 

Well the check engine came on today not sure why but it did, probably for the pre cat sensor.

 

How are NGK o2 sensors? I can get one cheaper than the mopar one so thats why im asking.