Help with high carbon monoxide emissions

[Max]

Italian tune up?

If driven hard here and there, the plugs shouldnt be black at all.

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That's kinda hard since it has no MOT lol but I did try to thrash it a bit before the MOT last time.

[Max]

If it passed the lamba test then the fuel mixing will be correct hence the passing.

Check everything else, timing, plugs, egr clean, Intake clean.

Make sure they aren't testing again a UK spec prelude. It should be tested against a standard jdm value or else it will never pass.

Timing and plugs has been checked, egr was cleaned out over a year ago, I think I cleaned out the throttle body but I can check that again.

Oh really I never asked them to test against a jdm value, that may help

[Max]

Hi Max,

Maybe this is wild shot but I guess its a cheap solution if it works.

Had problems getting my Motegi to pass the emissions test post a new exhaust. put some "Cataclean" in the tank as per the instructions and it passed the next time. use it now every time prior to an MOT. ( Have two 5th gens)

Here on amazon -


Prelude Pete

To be honest im reluctant to try that since the CAT is only 8 months old but ill keep it in mind.

[Max]

I always fill the tank with v power, add a bit of redex and take her out for a good spin before each MOT - works every time (for me anyway). Not saying that's gonna fix your issue but for about £3 and fuel you'll buy anyway it's worth a shot.

I always fill up with V Power and I did put a bottle of Redex through last year so I suppose I could try that again.

[Max]

Does it need a lambda test being a jdm car?
I thought the limits were bigger for jap cars hence the smaller cat

I wasn't aware of this, ill get the retest done against a JDM car

[stinkypaul]

I second Cataclean and an Italian tune up. Up to you if you risk that without an mot.
I once had a car that wouldn't pass emissions so I fitted hotter plugs for the mot, it drove a bit lumpy but it passed easy after that. Change back to normal plugs after the mot though. Ideally you want to get to the bottom of the problem but if the hotter plugs work it will buy you some time.

[Max]

I second Cataclean and an Italian tune up. Up to you if you risk that without an mot.
I once had a car that wouldn't pass emissions so I fitted hotter plugs for the mot, it drove a bit lumpy but it passed easy after that. Change back to normal plugs after the mot though. Ideally you want to get to the bottom of the problem but if the hotter plugs work it will buy you some time.

Thanks for the input, id rather get to the root of the issue than put a band aid on it but ill keep it in mind, thinking about it as I've already put a bottle of redex through, replaced the fuel filter and cleaned the injectors i doubt that would make any difference, so if anything i would consider this cataclean but then the cat is less than a year old, urrgh i don't know...

[Max]

Ok so i just went to check the FPR and immediately found a problem, not what i expected though which was either fuel in the vacuum hose or a blockage in the return line, as soon as i put my hand on the FPR it moved. It was bolted down, just not tightened down and i could jiggle it a little bit, i took it off anyway just to check the o-ring which seems in great shape, put a dab of oil on it, bolted it down correctly and connected the hoses back up, no more jiggling. This can only be my fault from when i took the fuel rail off to get the injectors out and clean them before last years MOT

Question is though could the issue have been as simple as this, and how did fuel not find its way out from between the fuel rail and regulator, i guess the o-ring just about held it back but how else would this effect fuelling? Could it have worked itself loose over time to create this issue?

Back on the subject of the emissions values again, 2017 MOT results:

Fast idle
CO < 0.30%vol
0.38%vol FAIL
HC < 200ppm vol
64ppm vol PASS
Lambda: 0.970-1.030
1.026 PASS

2nd Fast idle
CO < 0.30%vol
0.20%vol PASS
HC < 200ppm vol
44ppm vol PASS
Lambda: 0.970-1.030
1.023 PASS

Natural idle:
CO: < 0.50%vol
0.49%vol PASS

2018 MOT results:

Fast idle
CO < 0.30%vol
0.86%vol FAIL
HC < 200ppm vol
138ppm vol PASS
Lambda: 0.970-1.030
1.023 PASS

2nd Fast idle
CO < 0.30%vol
0.80%vol FAIL
HC < 200ppm vol
95ppm vol PASS
Lambda: 0.970-1.030
1.013 PASS

Natural idle:
CO: < 0.50%vol
0.63%vol FAIL

What i don't know is what happened to these numbers when i went for the retest as at that point the plugs had been cleaned and re-gapped and a new air filter fitted along with fresh oil. All i know is there was a minuscule improvement in the CO reading and a bit less fuel smell.

Both the CO and HC have doubled but HC is still within limits, high HC as far as im aware indicates raw fuel and high CO indicates incomplete combustion so seems to point to a rich fuel mixture which then resulted in unburnt fuel?

Anyway i just took her for a test drive, i don't know if its in my head but she seems to pull easier from low rpm when before there was some hesitation until around 2500rpm, i dont see any more smoke/mist through vtec although it was quite sunny just now so its hard to tell, and overall she seems to pull smoother. I swear she idles a tad lower, say 50rpm and when i hold the pedal at high idle, say 2000rpm she holds more steady, there is a tiny bit of hunting but its barely even 100rpm. Also had a little sniff of the exhaust after the drive and i don't think i can smell anymore fuel...

Surely this tiny change cant be it, what do you guys think, try another test? If it works i will be amazed

[Scott560]

I'd say if the fpr was able to wobble, then the ability for the spring to control the pressure would be adversely affected.

Enough to effect emissions? Hard to say, if it feels better then it's almost certainly going to help matters.

Since the plugs were blackened through overruling I'd say you'd found the culprit...

Lucky it hadn't let go in a more serious way!

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[wurlycorner]

Wow you've done some proper detective work on this one so far, well done to you!

Both the CO and HC have doubled but HC is still within limits, high HC as far as im aware indicates raw fuel and high CO indicates incomplete combustion so seems to point to a rich fuel mixture which then resulted in unburnt fuel?

I would agree with your surmising there.

I think it would still be worth you checking the timing, even if it was done a year ago - don't rule it out until checked and confirmed ok.

Even though you've re-gapped the plugs correctly, considering they are an 'after market/upgrade' design, it might be worth changing them for a standard set of plugs? Sometimes cars are very picky about the type of plugs installed (just a slightly different nose length etc. can affect the combustion in a bad way).

Also you mention the idle control isn't great, so I suggest plugging away until that is sorted. vanzep and nafeman have some threads about them hunting down poor idle control, over a long period of time until they eventually got to the bottom of it, those might be worth a read for some ideas?

You say the exhaust has been changed - what's the details on the exhaust? What has been changed from standard and to what?