Golf Mk7 TSI Petrol Engine failing NCT test for High CO Emission

pato11

Hi everyone,

I have an approved used car (Japan Import) purchased 2 years ago and I had the first NCT test 2 weeks ago and it failed (service done a week before the test)

I put dipetane and drove in low gear and still failed with the same exact numbers.

The engine light came on 3 months after I purchased the car and the dealership changed the lambda sensor. I remember the light came on again for O2 sensor signal stuck rich bank 1 sensor 1 but the code was cleared.

I talked to Auto Exhausts in Dublin and they told me (without inspection) it is the TSI engine and the car needs to be re-programmed.

I went to the VW dealership and they told me it needs a new CAT! I don't recall any performance or issues with the car (except occasional jumps in the morning when I first start and move the car)

The car is around 94KM so far. The car has twin centre exhaust which seems to be not the original.

Any idea what is wrong here and any decent place that can look at it properly (anywhere in Dublin, Kildare, Laois, Wicklow, Meath)?

pato11

More info

it is Golf 2017 TSI 1.4 Petrol Engine

User1998

I was actually in Auto Exhausts the other week and saw someone with the same car fail on emmisions and Auto Exhausts were unable to fix it. They suggested a Lambda sensor but you’ve already had that changed

pato11

https://www.boards.ie/discussion/comment/122366551#Comment_122366551

Good to know. I thought they spoke in confidence when they told me it was the software without inspecting the car!

Muppet Man

Daltons in Portlaoise. Not much they dont know about VW TSI engines.

TheDamIrish

Buddy had same issue - changed oil/new filter(will also address if issue with PCV valve), replaced air filter and cleaned the area around the throttle plate. Give it a good Italian tune-up before dropping it off at the test. Worth a try.

pato11

https://www.boards.ie/discussion/comment/122366710#Comment_122366710

I changed the oil and filter just before the test. I also gave it a few Italian tune-ups for hours before the test, and I almost felt the engine was about to explode with the high RPMs :D , but it still failed :(

https://www.boards.ie/discussion/comment/122366671#Comment_122366671

Thanks, will give them a call!

TheDamIrish

https://www.boards.ie/discussion/comment/122366770#Comment_122366770

Most likely a sensor out a whack so. Doubt the cat needs replacing. Hope you can find the solution.

mk7r

It needs a new cat

User1998

https://www.boards.ie/discussion/comment/122368572#Comment_122368572

Me personally I’ve never seen a mk7 need a new cat. And that auto exhaust crowd are very good when it comes to catalytic converters and even they said its probably not the cat. Might be worth trying tho for the sake of €250

pato11

So I visited Daltons in Portlaoise, and judging by the NCT report, they said it will probably need a new catalytic converter. They are very busy, so they won't be able to help before my NCT due date.

The guys at Auto Exhaust didn't inspect the car but they told me not a cat issue. So far, only the dealership has done the inspection.

Pops_20

I had similar issues with my car lately. Only your CO is over the limit. HC is very low so I don't think it's your cat at all.

Lambda is bang on 1.00 so I doubt there is a sensor issue. It's possible the probe wasn't inserted far enough into the exhaust. The fact that it is not a stock exhaust could also be a problem. It's a twin exit exhaust, but the stock one would be single?

pato11

https://www.boards.ie/discussion/comment/122368886#Comment_122368886

Not entirely sure but I would say so!

I used my obdeleven for some live data

https://streamable.com/bzn9ru

mk7r

https://www.boards.ie/discussion/comment/122368683#Comment_122368683

From the report it cant be anything else. The lambda as measured by the external NCT probe is bang on 1 so their cant be a sensor issue, fuelling issue etc its right where it needs to be.

The only job of the cat is to reduce the CO content of the exhaust gasses and if the lambda is correct then its just not working efficiently enough anymore.

Its possible the cat has been damaged from running rich in the past or an ongoing oil burning issue. It may be possible to just get it to creep through the test using something like vb26 but that would be purely masking the underlying issue of the car being damaged.

mk7r

https://www.boards.ie/discussion/comment/122368886#Comment_122368886

The cat has absolutely no relation to the HC readings at all, it is only there to reduce CO content.

blackbox

https://www.boards.ie/discussion/comment/122369049#Comment_122369049

The common 3-way catalytic converter reduces nitrogen oxides and oxidises hydrocarbons and carbon monoxide.

pato11

Thanks everyone, it looks like 2k for a new cat :(

Luna84

https://www.boards.ie/discussion/comment/122375389#Comment_122375389

Is that OEM? You can get cheap ones but they are crap. Might pass this NCT but would need to be changed next year again unless you are lucky.

pato11

https://www.boards.ie/discussion/comment/122375446#Comment_122375446

Yes it is from the VW dealer. I heard that the aftermarket ones are crap and will not last long

User1998

https://www.boards.ie/discussion/comment/122375708#Comment_122375708

They don’t but they are only €200

https://www.boards.ie/discussion/comment/122375708#Comment_122375708

Why would you go to a dealer, the bill is only 2000 quid because of that.

You can get cheap aftermarket cats that don't last long but you can also get good aftermarket ones that do

pato11

https://www.boards.ie/discussion/comment/122375834#Comment_122375834

Any recommendations for a good aftermarket brand?

User1998

What about a second hand one from a scrapyard?

Luna84

https://www.boards.ie/discussion/comment/122375972#Comment_122375972

Go to an exhaust specialist like Souhans and they can recommend decent aftermarket ones. It is their game so they would know more about them than us on the internet.

https://www.boards.ie/discussion/comment/122375972#Comment_122375972

Bosal are a good brand

pato11

Thanks folks, I'll ring Souhans on Monday!