Ek9 NCT Emissions Failure

soxturf

Member
Joined
Jun 27, 2009
Messages
673
Hi folks,

Unfortunately my car has failed the NCT (Irish equivalent of MOT) due to an emissions failure. (Its failing on high idle).

I originally thought it was the cat an replaced it with a new cat but still no joy.

After it failed the second time, the nct tester said that the emissions are fluctuating wildly, both up an down, above and under the required limit.

I replaced the 02 sensor an reset the ECU. I checked the voltage of the new 02 sensor an it is staying between 0.5 and 0.7. Obviously it should be fluctuating between 0.1 & 0.9. Just incase the new 02 sensor was faulty, I tried another new 02 sensor an checked the voltage again. It is still staying between 0.5 & 0.7. When I let the car out or accelerate hard, the voltage can manage to go outside the 0.5 to 0.7 range, but for the most part, especially when just idling, it is staying stuck between 0.5 & 0.7 meaning it is telling the car it's running rich an needs to lean up, which it obviously is not doing properly as the emissions fluctuate wildly an then it fails on high co2 meaning running rich.

Has anyone else ever seen their 02 sensor behave this way or had the same problem?

I own the car 13 years an never plan to sell it so this is cracking me up. Its not my daily, so now its just sitting in shed connected to trickle charger. Really want to get it back on road as I have big plans for it.
 

Civicfacelift

ej9 and eg6
Joined
Jan 15, 2011
Messages
609
Is there an additive you can put in petrol just for test ? or a more restrictive exhaust ?

That's just covering the problem though, if its running rich you will need to find the real cause.
 

ScottEk9

N.A King
Joined
Oct 27, 2006
Messages
225
Hi folks,

Unfortunately my car has failed the NCT (Irish equivalent of MOT) due to an emissions failure. (Its failing on high idle).

I originally thought it was the cat an replaced it with a new cat but still no joy.

After it failed the second time, the nct tester said that the emissions are fluctuating wildly, both up an down, above and under the required limit.

I replaced the 02 sensor an reset the ECU. I checked the voltage of the new 02 sensor an it is staying between 0.5 and 0.7. Obviously it should be fluctuating between 0.1 & 0.9. Just incase the new 02 sensor was faulty, I tried another new 02 sensor an checked the voltage again. It is still staying between 0.5 & 0.7. When I let the car out or accelerate hard, the voltage can manage to go outside the 0.5 to 0.7 range, but for the most part, especially when just idling, it is staying stuck between 0.5 & 0.7 meaning it is telling the car it's running rich an needs to lean up, which it obviously is not doing properly as the emissions fluctuate wildly an then it fails on high co2 meaning running rich.

Has anyone else ever seen their 02 sensor behave this way or had the same problem?

I own the car 13 years an never plan to sell it so this is cracking me up. Its not my daily, so now its just sitting in shed connected to trickle charger. Really want to get it back on road as I have big plans for it.
Did you find the problem? Be good to know for future reference.
 

civicx3

Drop a gear & disappear!
Joined
Jul 22, 2009
Messages
1,759
If you've tried different 02 sensors and they're both within range i would of thought its something else

Make sure the cat is hot, a cold or warm cat wont work properly and is it brand new or just new to the car? Aftermarket cats suck from what ive seen and dont last long, i killed a new one within a year

All fuel and air intake sensors wired correctly?
 

soxturf

Member
Joined
Jun 27, 2009
Messages
673
Is there an additive you can put in petrol just for test ? or a more restrictive exhaust ?

That's just covering the problem though, if its running rich you will need to find the real cause.
Hi mate, an additive might help if it was just barely above the limit and staying constant but wouldn't do anything for something like this. Even with a more restrictive exhaust, it still fluctuating so wildly that I don't think it would work. But yeah, like you said, I wanna fix the problem, not mask it :)
 

soxturf

Member
Joined
Jun 27, 2009
Messages
673
If you've tried different 02 sensors and they're both within range i would of thought its something else

Make sure the cat is hot, a cold or warm cat wont work properly and is it brand new or just new to the car? Aftermarket cats suck from what ive seen and dont last long, i killed a new one within a year

All fuel and air intake sensors wired correctly?
Hi mate, yeah what I was saying about the O2 sensor its that it should be fluctuating between 0.1 - 0.9, mine is only fluctuating between 0.5 and 0.7 so there is something wrong there but the problem is not with the O2 sensor itself as I have tried two new ones and both are doing the exact same thing.

When the car first failed the test I thought it was the CAT so I replaced it with a brand new aftermarket one. I know the CAT is good though as I used a reputable exhaust place in Ireland, and when my car previously failed the NCT about 5 years ago on emissions, I used their CATs to fix it and it went through every NCT until now (last time it failed on emissions it was normal though and it was clear the old CAT had failed as the emissions were remaining constantly high on high idle).

Thinking it was the CAT this time again, I replaced it and had it retested and it failed again, it was only after this I said to the tester that I was surprised as I had just replaced the cat, and this is when he said he does not think it is the CAT as the emissions are fluctuating so wildly there is clearly something else wrong.

I am about to embark down the road of checking all fuel and air intake sensors over the coming weeks/months and hopefully find the issue but I was just hoping that someone may have seen this issue happen before where the O2 sensor stays hovering around 0.5-0.7 and share what they done to fix it. Living in dream world I know haha :)
 

soxturf

Member
Joined
Jun 27, 2009
Messages
673
Did you find the problem? Be good to know for future reference.
Hi mate, no not yet, been working alot so have not had the chance to start checking properly but if I do find what it is, I will be sure to update so that the forum has it :) miss taking the car out at weekends so much at the moment! ha :)
 
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