Catalytic Converter is clogged?

[muzzle]

How will i know if my Catalytic Converter is clogged. i get only about 18 mpg thats with a 80% city and 20% highway.I think that its ok, but it seems as if when accerate real hard it eats gas like crazy. i only accerate real hard only once in a while to see what the car does but when i do it seems to eat about 1/8 of a tank of gas. i brought my 2004 impala ls about 5 months ago from a rental car company and i havent got a tune up or anything yet. Any help will be greatly valued.

[57chevyragtop]

Not knowing what engine you have it's a guess that you have the 3.4. Your gas mileage seems to be in the normal range with the driving mix you state. You have to realize stomping on the gas is going to use more...the car itself is 3400 lbs. with 180 horsies strugglin to get you goin...Not a good 1/4 miler by any means. Cats should not be confused with a lead foot. If it were clogged, you more than likely would have sluggish acceleration and around 12-13 MPG! avg.
A. keep your throttlebody and MAF (mass airflow sensor) clean.
B. Air filter should be clean, if not replace it. if you can't see through it when held up to a light bulb it's time.
C. 30 psi is tire pressure recommended by mfg., keep that checked monthly. I personally run 32 front 32 rear. 34/34 on long trips of 300+ miles. I get 34 mpg highway only! 70 mph avg.
D. Use good 5w30 oil and change filter and oil every 3000-5000 mile synthetic can get you 7500. $$$ Biggie Bucks for a non performance car.
E. Enjoy your ride....Dave

[INF3RN0666]

I was wondering if my CAT was clogged too. If you have a lead foot, it's unlikely to be clogged. After all, CATs only clog if you idle for long times or if you drive like a grandma all the time. Your gas mileage is actually good for city driving. The car is rated for 24MPG isn't it? So if you do 100% highway, you would probably get 24 MPG. Nothing wrong with the cat.

If you have the 3.4L engine, the HP and torque are fairly low AT BEST for such a big car. The 3.8L is poorly tuned too and you only get 200 HP and i think it's 200 for torque. Even then, that's really poor for a huge engine. By comparison, the 3.5L 2000 intrepids do 245 HP, which is a big difference from a smaller engine. Therefore, this aren't drag strip cars, but if your transmission is healthy, you can probably tune the engine or super charge it or put in a higher flow filter. obviously you'll get lower gas mileage but you can't have the best of both worlds.

[muzzle]

I didnt mean 80% city. i meant more like 60% city. i dont live in a city with alot of stop and go driving that why i was a little worried about it. where can i go get it checked out at? i seem never to get 20mpg and i know i should be getting more than that. i even use my cruise control as often as possible. what can i do about it