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The car in question is a 1.6i 145 twin spark, it has barely done 20,000 miles but just failed its MOT on emissions. since then a couple of people have looked at it and replaced various parts that usually cause this sort of problem but have both come back puzzled.

Any ideas of what to try next?

The obvious thing is to replace the catalytic converter however this has already been done with a non genuine part and it hasn't helped would a genuine part be any better?

Thankyou in Advance:)
 

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What has already been changed? The most common items to be replaced for this kind of failure is the Lambda sensor followed by the MAF sensor.

Also, it helps to give the car an "Italian tune-up" immediately prior to the MOT (drive it hard with lots of high revs in each gear). This helps clean deposits from the engine and exhaust, especially if the car isn't used much which it sounds like yours hasn't.

Filling up with a tank of high octane fuel (or using some injector cleaner additive into the fuel) before the MOT will also help.
 

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don't use supermarket petrol because that can really clog the engine up.
Ha ha...guess what I put in mine :lol: Need to get my club card points and 5p off a litre with my vouchers :D Seriously though, since I bought my car back in 2005 I've only ever put Tesco petrol in it with the odd few exceptions being when I've been somewhere without a Tesco in the near vicinity. I have to say that I've never heard of supermarket fuel clogging up engines before :confused: My car has always been spot on with the emissions at every MOT I've taken it too in the last 6 years so the Tesco fuel can't be doing the engine too much harm :cool:

The ECU is mapped for 95 RON fuel but it doesn't hurt to fill up with the odd tank of 98/99 RON and then take the car for a blast to clean the internals up a bit :)
 

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:lol: i haven't got one close. got asda, morrisons and co-op and i find that i get about 5 mpg more. smoother running and sound :) i do like hearing it sing now and again
 

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Yes.. my bet would be the lambada probe, if that hasn't been changed already.

Also, stick 250ml of parafin (aka "kerosene substitute" ) in the next full tank, to shift any gum and varnish... but clogged anything shouldn't affect emissions since the car can compensate for it up to a point by altering the mixture and timing etc. It's got to be a duff lambda... or potentially (seems less likely on such a low mileage car) a spot of corrosion on the relay that operates it, or its heater circuit.

Does the beast idle a bit lumpy?

Does the idle get better or worse after you go over 3000rpm?

Any variance here means it's the lambada'..


Also, clean out the MAF with some Contact Cleaner spray - gum on the little sensor will be making it tell the ECU porky pies about how warm the air is and what speed it's entering at... which will affect how the ECU is fuelling the car.

Ralf S.
 

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You don't want this....

You don't want this cause of emission failure but I have a 156 that failed MOT on emissions. ECU read, coils swapped, injectors swapped, injector cleaner through still failed. Did a compression test and there was none on number 2 cyl. Took head off and an exhaust valve edge was burnt away ?
Do a compression test and see if they are constant across al 4 cyls ? Hope its not though ?
 
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