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Discussion Starter #1
My car went for an mot on Saturday and everything was perfectly fine except the lambda readings. They were both reason too high? I had a full milltek system fitted last week with a precat decat and 200 cell sports cat. Just wondering why it would be failing and if there's any way around it? The lambda sensors themselves are new so I can't imagine it's a fault with them and there are no leaks in the exhaust anywhere so I'm stuck with what to do other than pay more for a dodgy mot lol
 

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Most decats will seriously effect emissions and I thought just as a rule if you the go the decat route, you might as well just class your car as illegal? I have absolutely nothing against it, I would do it too but it's all about emissions these days so always best to just keep the cat as it is if you wanna sail through MOT's etc
 

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Discussion Starter #6
as far as i was aware you could legally have just the one cat even though it is a sports cat? think i will just have to take to someone who will pass it
 

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It really depends on the sports cat you get, the car it's on and the person testing it. Basically, some sports cats are designed for tracks etc where the laws are a lot less demanding and basically sit right on the edge of legal and illegal. Every car gives off different emissions and some companies don't cater for every single car make model and year, so the emissions might be slightly over the legal limit and even slightly over will cause it to fail an MOT. Prob best just to get a dodgy MOT rather than shell out for a new one.
 

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The mot stations are checked and can re call cars to get re tested by vosa, when you fit a decaf you should be able to swap it out for the cat so bolts in and out for mot!
 

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Used to be as long as the emissions pass all is well and legal under new rules that come in 20th January this year they can legally fail car for not having a cat if it had one originally from factory ....mines a full cobra 3" turbo back de Catt system only just fails the test on hydrocarbons
 

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Discussion Starter #12
i will get a free retest and see what happens. do the old italian service ;) (redline it for a bit to clear the **** out)
 

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i will get a free retest and see what happens. do the old italian service ;) (redline it for a bit to clear the **** out)
If you get the engine nice and hot it will help a bit . A week old exhaust and sports cat won't have much crap to be cleaned out though , could worth checking your air filter and plugs .
 

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the technical answer is because the pre cat is gone and the sports cat is not as good as the original at reducing emissions the lambda sensors are reading that the exhaust is rich,
therefore the engine is actually running lean meaning more oxygen than fuel in the exhaust than normal = high lambda reading.
also if left un mapped (correctly) it will eventually melt your engine through running lean, also happens to be the biggest killer of the 1.6 turbo engine.

and yes the new mot rule means both should be there but if the tester didn't know that it had one in the first place then it wont fail, mot rules are subjective.
 
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