I often see garages advertising that they test catalytic converters. Is there a way of testing the CAT, or do they just mean that they test the emissions levels, and then if they fail assume the CAT must be to blame?
Surely to properly test an individual component would require it to be isolated, and then in the case of a catalytic converter, pass gas of a known composition through it and measure the output? Is that what is done?
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Cliff
I reckon this is just a 'standard' emission test, a bit like the 'pre-MOTs' that used to be popular as a way of drumming up business. I don't believe it's likely to be any more sophisticated than that, and as catalysts only work at high temperature a standard gas test would be difficult. Some measure of their effectivenes can be judged from the results as a properly functioning CAT will produce very low levels of the measured emissions. As you say emission faults may not be the CAT, but could be faults in related components. The ability of individual garages to carry out a proper diagnosis of faults will perhaps vary. I've certainly sucessfully advised a friend of my daughter to try the injector cleaner plus italian tune up to 'cure' his car that the garage reckoned had a faulty cat!
JS
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I suspected as much. I asked because it occured to me it would be in theory possible to do a proper specific test. Get the engine properly hot, turn the crankshaft to a point where a cylinder's valves overlap, and then inject a standard mix of Nitrogen enriched with a small quantity of the usual excessive combustion products into the air intake. Measure the result at the tail pipe, and print out as a relative % efficiency of clean up. Nil would be totally u/s, 100 would be as good as new. It could measure back-pressure too while it was about it, to detect clogging.
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A very good question, Cliff.
The answer is, really, what the purpose of the catalyser is.
You could give all sorts of prescriptive, analytical definitions, but I suggest that it's function is to deliver exhaust gas emissions with gas concentrations such that they will satisfy an MoT tester.
If it does, it's OK. If it doesn't it's not. Many folks would then just change it rather than ask whether any other component could cause similar symptoms, like a lambda probe. This is an item costing tns of pounds, rather than hundreds. When it fails some testers just blame the catalyser. And, if you're thinking further, has it really failed or is a connection grubby.
5-why analysis. Keep asking why and you get to the root cause.
Well done,
Sean
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I take it that you are refering to MOT testing station adverts where "Cats tested" is mentioned. This is a throw back to when the "Enhanced emmision test" was introduced by the then Department of Transport. The gas analyser had to conform to a standard laid down by the department, which was basically a four gas tester (carbon monoxide, carbon dioxide, hyrocarbons, and oxygen.) The software was designed to do the required calculating to get a "Lambda" reading, and also was to be an automated test programe. (Ie It would give a pass or fail result, it was not left to the tester to decide.) At the time there was no compulsion to have to own a four gas machine, but if the testing station had one, a sign had to be displayed stating "Catalyist tested" alongside the "MOT" sign.
So "Catalyist tested" has stuck, a bit like saying MOT when it should now be a VOSA.
As for testing cats, there are two main ways to test them. By close examination of the gas readings, and also by measuring the temprature of the catalyist. The trouble with measuring them is that they often are fitted with heat shields, so can only be measured at the outlet pipe.
Out of interest, testing stations do not have to own a Diesel smoke machine, hense "Diesels Tested" sign displayed for those that do.
Regards Tony
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