MX5 emissions

[Olds]

D'oh!
The MX5 had it's mot yesterday and failed.
Not on a lot, well actually only one thing. The emissions so I suppose I should be grateful, as on a seventeen year old Mazda, it could have been worse.
Fast idle CO reading was too high (0.59%) but he lambda reading was spot on (1.0) and HC reading good (49 ppm), so it looks like a new catalytic converter is needed.

[Manky Monkey]

I wouldn't have a clue how to remedy emmisions. Fortunately my Pop was tested on the age of the engine, so just the very basic emmision requirement.

[Archie]

try an Italian tune up first - 9 times out of 10 when we had cars fail a tin of engine gunk rubbish and getting the car nice and hot was enough to get it through. Especially if you're that close to passing

[Olds]

Did that. Didn't realise it would do 55 in second. Went back and slightly better but not enough. Think the cat has a slight rattle so is possibly starting to break up. The whole exhaust system while not leaking is not in the best of condition and wont come apart without help from Mr Grinder, so I will replace the lot.

[Olds]

Got the old exhaust off and I'm astounded that the emissions, while not being good enough, were as good as they were.
There is no catalytic converter ! Well there is and there isn't. The casing is there, but the honeycomb  inside, isn't !
Just waiting for the rain to stop so I can fit the new exhaust system without getting wet again.

[Manky Monkey]

Deliberately removed Dave, or just burnt away?
I really don't know anything about "cats". How exactly do they work? Do they just absorb particulates, like a filter?

[morrag]

From my schoolboy chemistry, back when Chemists were still called Apothecaries! a catalyst is an element or compound which, during a chemical reaction, increases the rate of change of that reaction without itself permanently altering. In the case of the internal combustion engine, removes some of the "nasties", such as Carbon Monoxide etc, from its exhaust gases....Morrag

[Manky Monkey]

So a chemical, rather than physical filter then? How does that work in practice? A perforated tube baffle that the particles pass through, breaking them down to an acceptable level before they leave the exhaust?
Just curious cos I've never worked on one.
So why do the boy racers remove them? Just to make the exhaust more free flowing & release many hundreds of extra horses in their 1 litre Corsas?

[Stix]

https://www.youtube.com/watch?v=nM9mdY10ZTU  lets you know how they work with a video

[morrag]

Nope, it's not filtration, it's the ability of a catalyst, in the case of combustion emissions a compound/alloy of platinum, to chemically modify a dangerous gas, CO, and change it to a non dangerous state, whilst the catalyst remains in its original state. A purely chemical reaction, called  redox......more or less

[Olds]

 
Think mine had just disintegrated. It was a genuine Mazda unit, so was probably the original. Close on 100,000 miles isn't to bad for one of these.
 Boy racers remove them as it's a lot cheaper than buying a free flowing sports cat and makes the exhaust slightly noisier. Probably very little  performance gained by removing it. A bit like using a dustbin as a silencer, it's wot we duz init. 

[the coppersmith]

If you remove the cat you will fail emissions at MOT time, many of the "younger" element near me, replace the cat at MOT time, and then remove for 12 months. Those cats are worth a lot at scrap time and local villains are knwn to take certain large cars and pinch the cat only, then abandon the car. Big Merc's by all account have huge cats, according to the grapevine 

[Olds]

A few years back local ambulances that were not on duty (service, cleaning,restocking etc.) had their cats cut out over night. Caused a LOT of problems and put lives at risk. The amount of platinum, palladium and rhodium used now is not as much as it used to be, but they are still a target.
Anyone nicking the cat from my MX5 would have been very disappointed.

[Manky Monkey]

Same thing happened to the Post Office Van fleet Dave. Probably the same low life's as our yard's just up the road from the ambulance station. Also had the diesel storage tank drained twice.

[Olds]

What you should and what you should not see looking into a cat.