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Catalytic Converter Life Expectancy

I have 1994 Toyota 4runner that I bought new many years ago. It has 226K on it and seems to have been a little less powerful at highway speeds (70 mph and above) over the last couple of years. Tuning and other maintenance (air filters, etc) are done regularly. My mileage is not what it used to be also. Used to get about 19 mpg and noted a bit above 16 mpg on last fill. There are no rattles in the converter and I have never had that “sulphur” smell from the car. As a matter of standard maintenance, how long should a converter last? Should I just plan on changing it? What is the normal life expectancy of a converter?

Converters should last the life of the vehicle. You can prematurely kill one but keeping a car tuned and maintained should keep the catalytic running fine for well past 300k miles.

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Converters do not wear out and should last forever. Or until they develop a rot hole.

The only “functional” part of a converter is a ceramic open-ended honeycomb with a platinum-palladium coating. It functions by converting any bonded nitrogen and oxygen molecules that come into contact with the hot plstinum-palladium into nitrogen and oxygen seperated. The freed oxygen is then caught by the passing CO to creat CO2 and the passing unburned HC molecules to “combust” into CO2 and H2O (ideally).

The only two modes of failure are coating of the ceramic with deposits from excessive oil consumption, which prevents the molecules from touching the platinum-palladium and stops the converter from performing, and physical destruction (crumbling) of the ceramic, which can block the flow of the exhaust. Crumbling of the ceramic is rare in today’s converters. If you had crumbled honeycomb restricting your exhaust your performance dropp would be dramatic.

So, if you’re not burning excessive oil and the ceramic is not crumbled, the converter is everlasting.

The sulpher smell is irrelevant.

If it were me looking for the source of little less power and slightly lower gas mileage on an engine with that mileage I’d start with a compression check. If the compression were good I’d probably want to get a scope and look at the ignition traces to see that the amplitude and form were good. If those were good I’d look to fuel pressure and finally the injectors.

My guess is that the compression will come in low. That does not mean the engine is worn out…only that it’s worn. Worn is not a bad thing. It’s normal in all things.

Post back with your results.

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I would run a compression test to make sure that the engine is not getting weak. If the compression tests fine then I would use a vacuum gauge to determine if the converter is clogged to some extent.
If you have a compression test performed you might post any numbers back because some people, including mechanics, will wrongfully assume a low reading is actually a good one.
You should have readings in the 170ish or more range.

It’s quite possible, and often true, that the honeycomb in a converter will partially clog and cause some performance problems, including loss of fuel mileage.
If the converter is gutted or a hunk of that honeycomb is broken out this clogging can often be seen on the leading edge of the substrate.

With proper maintenance to your car, the life of the car. With poor maintenance, then it will be a lot shorter, bot the life of the converter and the life of the car, although the converter may well be first.

Cars don’t improve with age…They simply wear out…At 226K miles, you can expect your Toyota to getting a little tired. Any muffler shop can test your car for excessive exhaust back pressure. But they won’t. They will say "Why take a chance?? We can install a brand new one for $XXX and then you won’t have to worry…

A converters life-span is determined by what happens upstream in the engine. Even when they fail, they seldom plug up and cause back pressure…They just stop converting…

Man I have to thank you from the bottom of my heart, I have been on the internet for hours and have not come across one answer that comes close to yours, excellently written and fully informative with every detail of how the cats work, I keep looking until I see something that makes sense AND now i can rest happily, almost 3 hours and your the BEST!! thank you!!. RG.
PS. I would service the fuel injectors with Seafoam spray every 10,000 miles, spray one can at idle into the intake, shut off and wait ten minutes then start and drive it hard, I go on the highway hard up to the speed limit and drop back 30 miles per hour and go hard up to the speed limit for a good 30 minutes, my power band is intense compared to before I do this, I increased my mileage from 15 mpg to 21 mpg, tested by the same drive to work by filling up before the drive and as soon as I get back from work (120 miles round trip) with the A/C on!! I swear by Seafoam spray, I add 1 or 2 cans of the same liquid can into the gas w a full tank just for shits and giggles ($7 a can) total $24.00 and my mileage and power band are amazing, Thanks for the cat info again, Robert.