Failed on emissions, new cats??

Hi, Car failed it's MOT today on very high emissions, he managed to get it through (don't know how yet) but said it needs new cats. I fitted the TopGear boxes earlier this year but I'm just checking it is likely to be the cats or hopefully something else before I drop £800 on new cats. I haven't noticed any other normal symptoms, loss of power, drop in mpg etc but I have been using it for my slow commute over the last couple of weeks following an op. Thanks

I'm sure Demort will chip in when he's around though it's likely it could be either the cats and/or the lambda/C02 sensors. Mine at its last MOT struggled to get through on exactly the same though I've replaced the cats, sensors and boxes now which was a planned bit of maintenance. You should also try and make sure your car is up to full working temperature and that its had a good "Italian tune" beforehand. FWIW, the Topgear 200 cell cats are stated at £480 though you can get 911uk discount and you're advised to get some new lambda sensors (mine only has 2). If your exhaust clamps aren't badly rusted, it's a job you might be able to do yourself though budget for a pair of clamps as well.

Thanks, that price is a bit better, I was looking at the 100 cell 2.5's at £795. I think I replaced the lambda's too but I can't remember, i'll check my receipts. I haven't had any warning lights either, i'll scan it when I get home.

Mine failed emissions on a couple of MOTs. Cause tirned our to be leaking headers. Once these were changed it passed no problems. My cats are original, and my car's done >170k miles.

Think of the cats as a filter as thats basically what they do .. they get old and dont filter as well . This is normally on one bank though . There can be running issues which also effect the emissions .. too rich , too lean .. for me i would start with a fault code read out , then look at the adaptions and the switching of the lambda sensors before saying it needed cats . Im not going to argue with your garage though .. they seem to have got the cats red hot to get an mot pass .. that normally indicates the cats are a bit tired shall we say !

Thanks both No fault codes at all. Not sure what you mean about looking at the adaptions deMort? I checked the headers when I was under the car at the weekend, they didn't look too clever and the bolts looked like they'd sheer if I even looked at them any longer! I know they're a job I'll have to do sometime shortly so I might wait until some warmer weather and replace the headers, cats and lambdas then I'll know I'm all sorted for a few years.

Adaptions are what tells us wether the car is haveing to add more fuel per cylinder to maintain Lambda or reduce it .. richen or weaken the mixture basically. Lambda = correct air/fuel ratio The point is to show us if there is a problem .. the car can adapt to normal wear and tear but if it goes off limits (you can only increase the injector duration by so much ) then it shows a fault in something. Basically if a maf sensor was faulty and not telling the car the correct amount of air then the car would give the incorect amount of fuel . This will in turn damage the cats. What the outside of the exhaust looks like is not a problem .. if air is entering through a split then that can be . The basic problem to me seems like the cats are old and tired .. not filtering the emissions enough .. hence the need to get them pretty hot .. cats work better with a lot of heat . If your garage says its cats then im not going to argue I would argue if the adaptions were off or any actual value on things like Maf were wrong in my eyes .

Great, thanks for the reply. It doesn't sound promising but is there a way I can measure the adaptions? It doesn't mean anything to me but here's the before and after readings.

Oh and about the fuel, I've looked today and I think it is using more. Down to 20mpg from about 23 around town.

Im afraid those are the mot emissions checks .. the adaptions are found on a tester .. we talk to the engine control unit basically and see what its upto .. I hate to be blunt but the figures are for us lot to interpet or anyone thats into this stuff .. its boreing trust me .. and then figure out what the problem is ... your garage has already said its the cats so i would go with what they say. I dont like to question other garages .. i only do so when a fault hasnt been fixed .. i wouldnt like them questioning my work ! If you do have a tester that can see these figures then i can comment on them .

Thanks very much for your help. They're my trusted local garage I use for the MOT's. They're not a specialist and though I'd no reason to doubt them I'm thankful for a second opinion to put my mind at rest.

Having said all the that the car has been into Porsche today for its new key, they carried out a visual inspection and found that one of my brake calipers is obviously weeping fluid. Not sure how that got through the test!

That is pretty dam rare .. in fact i dont recall a caliper actually leaking in 15 years. Without pictures i cant really comment .. but its unusual to say the least . An mot though .. whilst the above is a fail then the mot is a pretty basic check .. its minimum standards and in no way should it be classed as a clean bill of health for another year . Sensible advise there and heres an example .. Brake pipes corroded are a fail if bad .. on an mot you are not allowed to remove any covers .. 996 suffer badly under the L shaped panel on the n/s .. you can have an mot pass one day as they cant see them and a brake failure the next day due to a pipe in this area letting go . A service Actually tells you the faults on a car ... its always best to get an Indy or an OPC to service the car .. thats mainly down to our knowledge . i service other makes of cars as Porsche owners often have other cars in their stable .. i do my job but i dont have the in depth knowledge that a specialist on these cars has .. I know Porsche inside out .. i dont know other makes the same and hence their foibles .

Thanks, yes I appreciate the test is limited in its scope. Here's the walk through. I checked it when I came home, the calliper was clean so they must have wiped the fluid off. The nipple was tight too but I don't if they tightened it, they didn't say. https://video.citnow.com/vxSS42SKS14 Ps the cables ties are a temporary fix 😊

Young man .. thats brilliant .. it also makes me sure im glad i left the OPC when i did so i dont have to do those walk arounds lol. I do like that mechanic though .. straight to the point main problem .. bleed nipple NOT the caliper .. its got rust under it .. a new nipple and a clear out under it should probably sort that leak. Now then young man .. i bang on here so many times about waxoil .. or acf50 if you prefer .. theres not an inch of it on ANY of your pipes .. Ill be tough here .. get that dam car waxoiled ! .. i want to see these pipes dripping with the stuff in the future .. undertrays off and get them sprayed . OPC DONT do this , this is an indy or a forum thing .. it WILL save you money in the long term . The rest of it is pretty much normal .. headlight lvl sensor .. if it works it works although a new bracket is pretty cheap .