Ok so I took the Tardis (E30 318i Touring(M40B18)) for an MoT today, and, shock horror, it failed. There's a list of stuff it failed on, but the most perplexing, is the exhaust system. Apparently you're not allowed to take a car for an MoT with an aftermarket exhaust on it. Its emissions were 3.75% when it should have been 3.50%. Is that bad? How can I correct this? Thanks chaps.

It isn't illegal to have an aftermarket exhaust, as long as it doesn't exceed the db limits ! The emissions are from the engine... A tiny trick is to remove the air-filter or purposely block a breather-pipe so the fumes aren't re-burnt (only for a short while though) !!

Best idea is to clean ALL the intake from filter to manifold, check the plugs/gaps and make sure the engine is warm before MOT ;)

Does yours have a CAT?

It doesn't have a CaT no, and as for the after market exhaust, I didn't mean illegal, I just meant they will fail it if it isn't stock. The guy at the test centre said that if it's louder than when it came from the factory it will fail. Mine is nowhere near the DB limit, it's actually pretty quiet compared to impreza wagons etc. Is that all I need to do then? just clean everything? What about fuel mixture does that come into it? I'm pretty sure it's running rich, it stinks of petrol and I reckon it uses a tonne more than it should be using.

Yep, if the mixture is rich then that'll throw it over... And tell those clowns at the Garage that they are not worth their wages, you could use a scaffold-bar (or anything) as an exhaust as long as it has a muffler FFS

Hmm, how can I adjust the fuel mixture? xD

Also, I have welded a brand new middle box onto the downpipe bit and then welded a bendy bit of pipe to the other side of that then welded my Scorpion Oval onto that. you don't think it should have failed for that? It specifically says:-

003 Exhaust noise is clearly in excess of that emitted by a similar vehicle fitted with a standard silencer in average condition [7.1.4]

There are a few more on there that I don't agree with also but I don't know wether they are right or not.

Do you think its loud?

If you disagree then tell him that you will appeal, because you can !

I did tell him that, it's louder than stock fair enough but like I say, I know of loads of cars that are much, much louder than mine. His response was "if it's not stock I can't pass it". Meaning I have to cut that Scorpion off and weld the stock silencer back on. I had to put the original suspension back on too lol cus he wouldn't test it while it was that low ^.^ I'm thinking about emailing VOSA to get their views on the matter, cus like I said before, there are a couple of things it failed on that I don't agree with.

Go for it... I've had MANY lowered motors at my local, they just place extra lengths on the ramps so they ride up without catching bumpers/skirts !! Muppets eh?

Yeah man. I agree with a lot of the fails, cus they make sense. But 3 or 4 are just ridiculous tbf. But anyway, any idea how I can change the mixture? Is it to do with the AFM? take the top off and twiddle about with the ratchet thing in there? I'm sure I read that somewhere a few weeks ago.

you could try disconnecting the MAF !

Is a MAF the same thing as an AFM? :S If not then IDK what it is xD

Yes... What it does is tells the ECU the speed and temp of the airflow.

Some muppets cross the plug terminals with a diode to fool the ECU into thinking the engine is cold and subsequently "over-fuel" the car to get a couple more horses!

Ah ok, so what would taking that off do? :P

Just disconnecting the plug might make it run like a pig, lets try cleaning all the intake system first ;)

Aha sounds like a good idea to me :)