Catalytic Converter 1996 C1500 4.3L

[markqc]

The Catalytic converter seems to be making a rattling noise like there is something inside vibrating. The noise only happens at certain RPM's when accelerating normally and when slowing down/down shifting. What is inside a cat conv. and does anyone know where to find a diagram. I assume the converter is rusting out from the inside. I can bang on the cat conv. when the engine is not running and get the same noise. BTW the truck has about 175KM with a complete original exhaust. What type of life can one expect from the original exhaust. My driving is mainly at highway speeds and mainly at least 15 mins per trip with the majority of trips 1/2 hour.

Thanks,
Mark

[98SilvyKid]

I would get it taken to the custom exhaust shop and have hem tighten the housing for a couple bucks. My family's Jeep Cherokee did that exact thing and the cat's housing body was just loosened. Catalytic Converters don't consist of many parts, the converter has the body, and inside the body is a type of filter consisitng of catalyst beads to filter exhaust atoms. A shop should tighten it as it may be a pain, but it doesn't take long at all. Hope this helps.

[amac209]

inside the converter is a ceramic monolith(honeycomb) with small amounts of different types of metal like platnum, palladium,and rhoidium. the honeycomb in your converter is broken apart and restricting ehaust flow. you should replace it as soon as possible and will notice better performance and mileage.

[98SilvyKid]

Intersesting, didn't know the catalyst parts could brake down so easily. A shop can check it out for you.

[J-Ri]

Originally Posted by markqc

What type of life can one expect from the original exhaust?

Depends on how close you run to stoichiometry (14.7:1 air/fuel ratio). I'd say with that many kilometers on it, it probably is time to replace it. To see if it's the inside or outside, just try to wiggle the heat shield on it. MAKE SURE IT IS COOL. The cat runs much hotter than the rest of the exhaust, and stays hot longer. You could burn you hand pretty bad if you touch it hot. If it's plugged up, it will be even hotter than normal. Give it AT LEAST and hour, then check the temp starting out at the tail pipe and working closer to the cat.

If you want to see if it (or any other exhaust part) is clogged, connect a vacuum guage to the manifold vacuum. Rev the engine to about 2,000 RMP and watch to see if the vacuum starts to fall over time. The vacuum should immediately drop to close to zero, and immediately return to normal when you snap the throttle. Takes less than half a second to drop and rise.

[markqc]

Thanks for your replies. It's funny you mention that you would experience loss of performance and mileage. I just noticed a loss of performance from about 2000 RPM and up in 3rd, 4th and 5th gears. Guess it's time to change the converter. (haven't noticed loss of mileage yet.)

Thanks
Mark

[markqc]

Had the converter changed and eliminated the loss of performance. Next question! It was recommended to change the O2 sensor as this may cause the converter to fail sooner. I rarely get the check engine light on so would assume that the O2 sensor is ok.(I hear that the causes of the check engine light are usually emission related) Any thoughts on this.

Thanks,
Mark

[bad68chev]

O2 Sensors response time slows down as they get older giving the computer less control over the engine. Usually reccomended to replace every 60,000 miles, especially if you see a decrease in fuel mileage. I had a fiero that was getting 15mpg, went up to 30 after replacing the 02 sensor and there was no check engine light on before replacing it!

[J-Ri]

You may as well replace them, even a small increase in gas mileage will pay for the sensors in no time.