Contour Enthusiasts Group Archives Forums General Troubleshooting How can i prove that my cat is bad?

Whats the best way to pin point a bad Catalytic converter, and bend ford's arm to fix it...i've checked and replaced all my 02 sensors (half the problem of my bad gas mileage), fuel filter, cleaned intakes, but i still get an egg smell and only ~250 miles to the tank with mixed driving. post away!

250 per tankful is the average.
Try a different brand of gas.
Some gasolines contain a high amount of sulfur,
paticularly TEXACO.

Any other symptoms that you notice besides the smell? Are your CELs completely gone? Is performance OK. Any heat in the footwell or plugged exhaust sounds? The rotten egg smell is sometimes due to unburnt fuel making it to the cat. When my cats went (both times), I didn't get the sulfor odor, but more of a burnt carbon smell, extra heat in the main cat, and crappy performance.

ehh, that 250 miles was after i put premium fuel mixed with regane fuel system "cleaner". I ran it to empty and now i'm trying Mobil 87 grade. It smells like sulfure every time i do a little "sprited" driving. I also thoguht these cars were rated at 20 mpg in the city? 250miles (actually closer to 230 when the 'add fuel' light came on)/14 gallon tank = 17.8 mpg max....to me thats seems a little low for a stock mystique with normal driving conditions and no higher than 4,000 rpm 95% of the time. am i just nagging?

I would say that is low. My gas light comes on at 300 to 310 with mixed driving and some spirited driving mixed in there. I average around 24 MPG. Something is up with your car!!!!!

You should notice a loss in performance if the cat(s) is/are plugged. I would say that your performance is probably hurting if you are only getting that kind of mileage.

A reputable mechanic shop can perform a backpressure test using a special pressure gauge made to hook into the exhaust pipe. The gauge is hooked in through a small hole drilled into the pipe before the cat, and after the test is complete, you pop in a special rivet that seals that hole. Anything more than a couple a p.s.i. during a roadtest under load, would indicate a restriction in the exhaust

The egg smell means that the converter is working. My car does it and my friends 02 Honda Civic does it. If I rev the engine alot it seems to go away. The converter will start to rattle when it is going bad. Also I had the same MPG problem as you so I changed my plugs and wire (Boush Platnium +2) and I get between 20-22 MPG with a pretty hard driving. I have a V6

Mine was rattling like a maraca before it was replaced.

Do a search on low sulpur gas for your state or province. If you use a low sulphur gas, it will get rid of that "rotten egg smell".

I use Sunoco here in Ontario as the 87 to 94 all have less than 200 ppm. Stations like Shell, imperial Oil/Exxon can have upwards of 1000ppm Sulphur content.

All road use gas will have to be less than 50ppm by 2005 anyway. As an interim, stations in will have to be about 150ppm or less by July 2002 (in Canada) but Imperial oil is Fighting this (*******s).

You guys in the Atlantic provinces have it good because Irving oil has their gas at below 50 ppm sulphur content already...

http://www.foe.org/
http://www.foecanada.org/

Can you guys elaborate on the cat rattling. I have a rattle in my exhaust when my car is first started and then it seems to go away when the car warms up. It is pretty nasty around 2000 to 2500 RPM within the first couple minutes of driving. Does this sound familiar to anyone??????

This is just one way a cat goes bad. Rattling cat means the insides are just breaking apart and the pieces of the core are rattling inside the cat's case. But this is just one type of failure that a cat can experience. Cat meltdown is another example of say, if you had something wrong with the engine and you were burning really rich exhaust out to the cat, and the excess hydrocarbons try to burn inside the cat converter, specially when the airpump switches to downstream mode, and then the Cat gets REALLY hot and the insides typically meltdown into a big glob of restriction that will hamper performance. And there are several levels between full failure restriction (eng wont even start) all the way down to partial restriction (engine just looses MPG and some power). A backpressure test will tell if you have a restriction which will cause loss of power. A cat that is just rattling or broken apart inside usually only makes annoying racket and wont pass emmisions, but will not usually pose a performance hampering restriction