Hi Guys,
First time poster, long time lurker! I have a 2011 NC2 roadster which I’ve had for a few years and love, it is lightly modified for track use (suspension, wheels/tyres, brakes, bigger rollbar, exhaust - not decatted). It has been so far a brilliant car however came up to it’s MOT just before all the coronavirus malarky and failed on high HC. I’ve included an image of the emissions test although seems their printer is terrible so figures below!
2nd fast idle
HC should be <0.2%, tested 0.6%
CO should be <200ppm, tested 61ppm
lambda 1.004
My understanding is high HC is due to unburnt fuel rather than cat issues - however I have noticed that my exhaust has been getting louder over the last few months and also popping and banging a lot more. Don’t have any warnings lights on, scanned the car using Forscan and all of the modules are happy, no codes. The car only does a few thousands miles a year but the majority of that is on track so does get reasonable abuse! Currently the engine is entirely stock. Doesn’t burn any oil, and performance doesn’t seem down however it does seem to have a bit of a ‘jump’ in performance which I’m sure didn’t use to be there around 3krpm
I’m a bit stuck as I can’t measure this fault myself which means other than checking a few obvious things like plugs (which look fine) I’m a bit stuck as to what else to test. Any suggestions would be welcome, or recommendations for someone East Midlands based how is open and suitable to sort and re-mot!
Mine failed early-March just before lock-down, but over the next week or so, I put on a different back-box, as the original was rattling (internally?), as well as running some Cataclean through the petrol tank ready or a fast motorway run. On the subsequent re-test it sailed through quite comfortably. The Cataclean cost me around £16 from Halfords and was well worth the money.
Suspect that the Italian tune-up isn’t what’s required here, as he mentions he takes it on track days now and again, so it doesn’t have the gunge build up which it might have if only lightly used.
Are you sure that you’ve read that emission report correctly? CO should be expressed as a percentage % and HC should be expressed as parts per million PPM. Has it not failed on excessive CO%?
I’d suspect a knackered or inefficient catalyst if that’s the case.
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Surprised there are no error codes showing.
HC at 61ppm passes MOT but way too high for healthy emissions.
We would not entertain warranty returns of cats where emissions report shows HC > 60ppm. At last MOT on my infrequently used 1997 MK1 1.6, HC was highest its ever been at 21ppm, 1991 Eunos, more frequently used, summit like 8ppm
CO percentage is way too high.
Lambda reading = fuel/air ratio looks well within range.
HC is basically soot so the top end of unburnt fuel output, CO is also a constituent of inefficient combustion.
If the exhaust has got louder I am wondering if the cat core material has been blown out?
These have two cats - maniverter at front and an underfloor cat. OBD, error code testing is just for the maniverter but MOT emissions would be looking at the exhaust gases that have passed through both cats.
High CO generally indicates a failed cat. Depending on the nature of the failure that may also be the cause of the high HC.
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I agree with Rhino. Those symptoms suggest a dead cat or two. Also every pop or bang can destroy another bit of cat.
Things to look at which might have caused this; MAF clogged, MAP unhappy, air filter clogged, bad spark plug or coil, and unlikely but possible a VVT problem. Test suggests engine temp sensor reading is OK but if low it would force a richer mix.
As above. The oxygen sensor certainly seems to be working correctly since lambda is correct. Seems like a cat problem, but it could be the issues noted by RichardFX. I’d concur that the catalyst does affect HC emissions. It converts HC into H2O and CO2.
JS
Thanks for all the comments, as roadster_robbie mentioned, now I look at the emissions sheet it does seem it failed on Co rather than HC. Although I swear the tester said HC to me … Let’s start the diagnosis again haha.
I think based on this I will at least get the manifold off and have a look at the cat, I have actually removed the secondary cat when I changed the exhaust. I assume if the cat has failed it will visibly look not right inside?
I think you have just answered your own question perhaps. By looking will not necessarily show or prove anything. The single Cat converter has failed for one reason or another.
Clearly something has changed as it has passed two previous Mots in its current configuration. Just wondered if a visual inspection would be worthwhile before just ordering a new manifold (I was planning on doing the BBR Super 180 conversation anyway so not the end of the world)
If yours has the original manifold then this is what you would be looking at which is all sealed up.
Hope you get it sorted soon to enjoy the lovely weather. 
Just to put your mind at ease this what you see down the Cat, i.e not a lot.
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Did you go back to a catted manifold? What was the cause of the high emissions in the end?
