[Mk2] [NA] MOT fail - emissions - help assessing level of failure

[Racer7]

Hi guys,

Put my UK N/A back on the road after a couple of years of being SORN I have failed my MOT on the dreaded emissions part.

I am currently assessing my repair list but before that I wondered just how off I am of passing.

I did think that the car probably wasn't hot enough. Had old fuel that perhaps hadn't fully burnt off.

One thing to know which is perhaps a big cause is previously when I MOT'd it the tester said there was some emissions leaking from the CAT and back box connection. It's Mongoose SS exhaust with the OG cat welded in a fashion to therefore be a cat'd aftermarket exhaust

Here are my results:

https://drive.google.com/file/d/1GYqXs5 ... sp=sharing

My instinct is to change crush gaskets and fit a new lambda - based on what readings seem to be most out and the info above.

Wondered what the thoughts of the experts are?

[SonicSW20]

Check the exhaust system for leaks thoroughly - even a small hole in the backbox somewhere is enough to throw the lambda value out a lot. You can test the o2 sensor with a multimeter (process in the workshop manual) to confirm it's functioning.

Agreed on the heat issue - As you can see on the 2nd fast idle test both HC and CO dropped significantly, suggesting the cat was not up to temperature. A good old fashioned Italian tune up just before testing will solve that.

[Racer7]

A good old fashioned Italian tune up just before testing will solve that.

Thanks for swift response. So the Italian tune is an actual thing. That's where you drive at high revs in first and second right? Someone suggested that speed is also quite an import part of it. Ie I can't just rev to 30MPH - not sure how important or true that part is.

Need to find a decent garage now to switch out the crush gaskets. I'm hoping that the car will get through on some minor changes.

[pbmr2]

All good advice above..

Stick some of this in the tank before the test day and make sure it's driven enough to pull though to the injectors by the test time.
This stuff works magic.
https://www.amazon.co.uk/Forte-Lubrican ... as+formula

make sure you get rid of the old fuel, it really doesn't help as it under-burns so high HCs

exhaust leaks are evil..

[Racer7]

All good advice above..

Stick some of this in the tank before the test day and make sure it's driven enough to pull though to the injectors by the test time.
This stuff works magic.
https://www.amazon.co.uk/Forte-Lubrican ... as+formula

make sure you get rid of the old fuel, it really doesn't help as it under-burns so high HCs

exhaust leaks are evil..

What is considered as 'driven enough'?

I'm wondering whether i should have insisted that they ran it again. But i suppose I'd just be putting off an inevitable problem.

[pbmr2]

depends.. how much old fuel was in the tank?
How full is the tank now?
If the old fuel was topped up with new, was super used?

normally it starts working after about 5 miles, have to add it before topping up with fresh fuel. helps the mixing.

[wilkie senior]

I would concurr with all the above, mine doesnt get driven too much, and i had the same at the last MOT

they put some wonder juice in the fuel tank, and I drove for a while all seemed ok a couple of days later

[mr2garageswindon]

Also with the high lambda, if you have a twin exit exhaust sometimes its worth blocking the other exit with a rag while doing the test.

[Racer7]

Thanks all.

I'm going to the tests Gazza_DJ recommends and see if i can just put some high temp sealant at the suspected leak point by the crush gaskets.

Feel like i should have insisted that the tester ran it again. not like I can now just borrow the equipment from someone to test it's in range!

I either have to move closer to Pacific Works/Drift Limits or they need to come closer to SW London!

[wilkie senior]

Check the exhaust system for leaks thoroughly - even a small hole in the backbox somewhere is enough to throw the lambda value out a lot. You can test the o2 sensor with a multimeter (process in the workshop manual) to confirm it's functioning.

Agreed on the heat issue - As you can see on the 2nd fast idle test both HC and CO dropped significantly, suggesting the cat was not up to temperature. A good old fashioned Italian tune up just before testing will solve that.

Good advice, this