NCT fail

LegacyGT07

LegacyGT07

Active member
ISDC Club Member
Hi guys,

Hoping someone can give advise.
Failed nct last week on one or two things, one being my emissions.

It says CO 0.45 vol % in the above 20% category.

Would an engine flush treatment be enough to bring it down or is there possibly more I’d have to do?
I wasn’t sure if the fact there’s not many of them around (Jap import Legacy GT) had anything to do with the fail as in if it would have been tested correctly or if that’s even how it works.

Any help is appreciated.
 
Ah the ould emissions chestnut, I do this dance every year and this year was the toughest. I'm only after passing last night on the third attempt.

What are your Lambda/HC readings? Low Idle?

.45 is not too bad (assume that's high Idle?) - for me attempt 1 was 1.39% CO, second test .7% and last night .09 (some serious difference). So you starting out at .45 is a good start I'd say.

Biggest factor I think is heat - it really has to be hot going in. I think I've failed every single time on the main test, and subsequently gotten through on retest. Difference being that for the main test the car is often sitting for 20-30 minutes out in the car park waiting to be tested so it's cooled well down by the time it goes in, whereas retest they take it in very quickly while still hot. Differing opinions on it but I do think Dipetane helps, supposed to run hotter (could be nonsense but anyway)

So what I did in case it helps:

First test - added a bit of dipetane to the tank (as per instructions on the bottle) Car was waiting easily 25 minutes before going in. Result 1.39 CO on high idle (low was fine)
Retest one - added a lot more dipetane (about a quarter bottle to half a tank). Drove on motorway, normal driving, gave it a good blast (slow down a bit, accelerate hard, repeat). Car was waiting maybe 3 minutes. Result .7% high idle. Better
Restest two - bought a bottle of cataclean, ran that through, filled up half a tank after and added quarter bottle of dipetane. This time for the last 10 mins on the way to test centre kept it in 3rd or 4th to keep revs up around 4k. Car was waiting about 2 minutes. Result .09 high idle.

So whether it was the heat, the additives, the driving it a bit harder with additives I don't know, just sharing what I did in case it helps you.
 
KrakityJones said:
Ah the ould emissions chestnut, I do this dance every year and this year was the toughest. I'm only after passing last night on the third attempt.

What are your Lambda/HC readings? Low Idle?

.45 is not too bad (assume that's high Idle?) - for me attempt 1 was 1.39% CO, second test .7% and last night .09 (some serious difference). So you starting out at .45 is a good start I'd say.

Biggest factor I think is heat - it really has to be hot going in. I think I've failed every single time on the main test, and subsequently gotten through on retest. Difference being that for the main test the car is often sitting for 20-30 minutes out in the car park waiting to be tested so it's cooled well down by the time it goes in, whereas retest they take it in very quickly while still hot. Differing opinions on it but I do think Dipetane helps, supposed to run hotter (could be nonsense but anyway)

So what I did in case it helps:

First test - added a bit of dipetane to the tank (as per instructions on the bottle) Car was waiting easily 25 minutes before going in. Result 1.39 CO on high idle (low was fine)
Retest one - added a lot more dipetane (about a quarter bottle to half a tank). Drove on motorway, normal driving, gave it a good blast (slow down a bit, accelerate hard, repeat). Car was waiting maybe 3 minutes. Result .7% high idle. Better
Restest two - bought a bottle of cataclean, ran that through, filled up half a tank after and added quarter bottle of dipetane. This time for the last 10 mins on the way to motorway kept it in 3rd or 4th to keep revs up around 4k. Car was waiting about 2 minutes. Result .09 high idle.

So whether it was the heat, the additives, the driving it a bit harder with additives I don't know, just sharing what I did in case it helps you.
Click to expand...
Just posted a photo of the reading above,

They took the car within 5 minutes of me handing over the keys so I was surprised when it failed i definitely thought it would have been hot enough :(

When I bought the car it came with a pass nct sheet that was a retest sheet so I’d say he definitely had to put it through a few times aswell..

Thanks for all that though very helpful, I’ll make sure to absolutely rally the car going up to the retest now 😅
 
Lambda is good, low Idle, HC all looks good (same as my own when it failed). If it were me I'd add dipetane and make sure it's very hot going in, keep gears down and revs high for 10-15 minutes even if it means crawling there in 2nd gear! Worth a shot. Keep us posted.

- just to add I'm only going by what's worked for me, plenty waay more knowledgeable on here than me so take their advice over mine!
 
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