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swmbo had her fiesta fail the mot on emissions so the garage fitted a new cat. Still couldn`t get it through though and after a few days of headscratching the mechanic took off the new cat and substituted another off a staff fiesta. car proceeded to pass its test. So the new cat was faulty , another was ordered, fitted and tested o.k. How can a new cat fail ? no active ingredients inside or possibly physical damage in some way ?
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If it's failing on emissions, then the cat isn't processing the exhaust gases properly, The only thing I can think of would be a failure in the plating process where the metal surface layer is placed onto the honeycomb elements. If this happened, the gases wouldn't react properly with the surface and the emissions would show high amounts of NOx, Carbon Monoxide and hydrocarbons, or all three.
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Cats can be damaged, but usually only when hot. The cat gets very hot and becomes brittle while hot. A good bang will break up the honeycombe elements while its like this.
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Not that unusual if it was an aftermarket cat. The cat is usually made from cordierite (ceramic) with an aluminium oxide washcoat of about 40microns thickness. The washcoat contains the catalytic metals (usually platinum-rhodium) plus stabalising materials like lanthanium, a 'rare earth' metal (not sure of the spelling of that one!).
What happens is that the washcoat is not properly applied, or often too thinly applied. This means that there is simply not enough exposed catalytic metal. There is also a lot of recycling of cats going on - obvioously a good thing, but can lead to quality control problems.
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Everyone's first reaction to poor emissions is to replace the cat, and I am assured that it is rarely the culprit. What sort of driving did the car receive in between fitting these replacements? Merely taking the car for a good thrashing after the first failure might have been sufficient. When the first cat was fitted, was the car properly warmed up before testing - properly as in driven hard for 20 miles?
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thanks for the help everyone. To answer Cliff, I doubt if the car was driven twenty miles before the retest, the car is only used for short trips of a couple of miles at the most . Criminal I know but given the choice of getting wet or wrecking every engine in Britain what would you expect most people to do ? Poor preperation on my part as well , an oil change and two new filters with an italian tune up might have helped a bit. I think the tester did do a warm up run on the road but only a couple of miles.He was getting a bit fed up of it, dunno why he couldn`t just stick the probe in a bucket of oxygen !
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Many modern cats are Palladium/Rhodium.
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What's the life-expectancy of a cat these days? Do they last as long as the car? (assuming it's not a short-journey only car)
Thanks
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Upto St.III emissions the manufacturer is required to demonstrate that the catalyst will still be working well(under controlled and near perfect conditions) upto 80,000k.and St.IV on it is 160,000k.
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What's the life-expectancy of a cat these days? Do they last as long as the car? (assuming it's not a short-journey only car)
283,000 miles so far. No problems with emissions.
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Nearly there, its Lanthanum, no 57 on the periodic table.
Pastyman..
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