leeorias

just started to hesitate when accelerating, but if I go slow it is ok, changed all th eplugs, wires, cap and rotor. I here a rattle in the area of the cat converter, could something inside have broken loose and is plugging the exhaust?? Fuel filter?? any Ideas

CrazyMacaw

Hi and welcome to CF. It would be helpful to know the year, make, model, and engine specs for your vehicle as well as any fault codes.

As far as the rattle in the cat area, climb under there and tap on the exhaust with your hand (when it's not too hot) and look to see if it's just the heat shield/cover that's come loose from rust. If everything is tight on the outside and you hear the rattle coming from inside the cat then its guts are loose and could maybe be restricting flow.
Hell tap on a few things under there and see if the rattle is unrelated to the exhaust.

leeorias

1998 jeep grand, 4.0 engine, I have felt it and the outside isn't loose, does this mean that the cat isn't working at all, can I replace it with a straight pipe?? CK engine light is on but oil and water and charging are all normal, I assume it has to do with a oxygen sensor, Obviously I'm guessing

CrazyMacaw

It doesn't definitively mean its not working at all.
I'm not 100% sure if replacing it with a straight pipe would be wise. I'm thinking maybe without it the extra hydrocarbons passing over the O2 sensor might make the computer think its running rich when it actually isn't. Maybe someone on here can answer that one more accurately than I can.
A new aftermarket cat I'd guestimate to be between $100-$150.
Keep in mind if you live in an area that has annual inspections or emission testing you'll probably fail without a cat.

You need to find out what's tripping the CEL.
Stop into an Auto Zone or Advanced Auto and ask them to hook up their code reader to it, they don't charge anything to do it and they will give you a print out of what the fault codes are. From there you'll have a much better idea of whats going on and in which direction to go.