I’m hoping someone can help with suggestions for a failed emissions test for our 2001 MK2 MX5. We are based near Cambridge and use our MX5 for trips and as a second car so not daily use.
We have tried the following: Replaced the Lambda sensor, new plugs, carbon clean, new seals on injectors but we are still not meeting the required limits. If anyone has any suggestions for things we can look at or a more specialized garage somewhere in the area we could try that would be appreciated. Its currently SORN awaiting MOT pass in order we can get it taxed and back on the road again. Just to mention also our CAT was stolen and replaced recently and appears to have been repaired properly so we were a bit surprised it failed the test.
Hi Gemma
Please confirm MK2 or MK2.5 and 1.6 or 1.8
Please put up a photo of the emissions failure certificate with all readings.
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Its a 1.8, I have asked the garage for a copy of the report and I will post it once we have it. The gas that is the problem is the CO. At idle all readings are ok but at fast idle the CO is .7 the pass level is .2 so thats quite a bit of. gap. We wondered that it’s running a bit rich? We need some new ideas at this point or a more specialized mechanic who really understands MX5´s to help us out. Any advice would be great.
OK, a MK2 1.8 I assume? Almost all 2001 cars are MK2.5 but almost all MK2/MK2.5 cars with emissions problems are MK2 1.8, Pre OBD and pre VVT.
It is unfortunate that these cars seem to have an inherent issue with emissions. Running fine, well serviced but possibly half of these struggle at MOT time with emissions and likely have for years. Is the car new to you or do you know its history in this respect? The MOT history can often give a few clues.
Did you fit a cheaper non type-approved aftermarket cat or the more expensive type approved with more precious metals and more of a chance of getting a marginal emissions car to pass an MOT.
Lambda should be close to 1.0, so .99 to 1.01.
HCC should be less than 20. MOT pass limit is stupidly high at 200 but as an example the cat manufacturer who supplies me will not accept a return under warranty where the HCC reading is above 60. Put simply HCC, hydrocarbon, is soot, which at a level of 60 or above will overwhelm and kill any cat.
Elevated CO only would tend to point at a failed cat.
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Yes it is a MK2 1.8
We bought the car last year, and its done very few miles and was dry stored for the best part of 20 years. The service records seem to show it passed without much issue. Thats interesting what you mention about the aftermarket CAT we were totally naive here its likely the cheaper solution. We would have spent more if we thought we might have these issues. We will investigate a bit further and I will post the paperwork once I have it. Thanks for your help!
Its more than likely the 02 sensor before a cat on these mx5’s at fault.
How often is she used and what distances ? how far is the your MOT station from you?
M-m
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Not if the issue is CO only. A precat lambda problem, the only one on the MK2, will cause fuelling issues upsetting both the lambda reading(rich) and HCC(hydrocarbon/soot)
Dodgy precat lambdas tend to result in over-fueling and general increases in the emissions of incompletely burnt fuel in its various forms.
I am surprised you didn’t jump on the all aftermarket cats are rubbish Wayne as that is your usual mantra. Again read the thread and you will see that an aftermarket cat recently fitted.
One more point; from my experience of selling cats and lambda sensors, cats are replaced far more often than lambdas and a failing lambda will often display an error code. A failing cat will not produce an error code on the MK2.
???
Why the attack ?, most after market cats are rubbish , but thats not the question i was asking the OP?
M-m
The CAT fitted is a BM Catalyst type approved. We talked to the local Mazda dealer and they said they have had to replace aftermarket CAT’s on these older cars as the component itself has failed. However how will we know if the Mazda specific part will definitely solve the problem? Are there any other likely issues if its not down to the CAT itself?
BM Catalysts type approved cat should have been the way to go.
You would have had a choice on the MK2, much cheaper non type approved or type approved, whereas the MK2.5 would have to be type approved most of the time as most registered after the type approval required date, 1/3/2001
You were going to get back with the emissions report?
Have you looked up the MOT history to see if any note of previous of emissions problems. Just type ‘MOT History’ into google and enter the reg. number into the government application.
Was the cat that you replaced original or aftermarket? If original would have had considerable worth, scrap. If aftermarket, you know it had already had to be replaced. The main killers of cats whether they be original Mazda or the cheapest aftermarket is a misfire leading to neat fuel igniting on the front of the cat core causing superheating and melting/breaking up or soot from unburnt fuel stifling and choking the cat, preventing the catalytic process and stopping the cat heating up properly. Cats need to get quite hot for maximum catalytic conversion effect and soot insulates them from the exhaust gases that facilitate that. One of the main reasons the car fitted with a cat needs to be properly warmed up for a fair emissions test. The process of killing a new cat where there is a problem can take a matter of weeks.
It does sound like there is a problem with the car. BM Catalysts use generic material for their cats, although all individual type approved cats had to be fitted to the specific cars and shipped to Spain for testing when type approval came in(2009). Whatever others may say, very rare for a cat to fail for anything other than a vehicle problem. At the end of the day, that has to be accepted anyway as no other choice; originals would be prohibitively expensive and not available new. Fit a used original item and it will be stolen at some point as well as offering you no running advantage over a type approved BM Catalysts cat.
As already mentioned, the clue to this is the elements of the emissions report, so lambda reading, HCC ppm and CO percentage. You have already mentioned the CO failure but not the other emissions criteria. These will give some clue as to the problem regardless of whether they are MOT pass level or not.
There are no previous issues with emissions and the garage won’t send us a copy of the emissions report we suspect they have lost it somewhere, they tried to charge us for a copy then couldn’t find it. The CAT we replaced, as it was stolen as previously explained and it was an original part. According to the local MX5 dealers they have had issues with these aftermarket CAT’s failing and replaced them as a result. However new parts should be under warranty so we have sought to check that first.
We have been through every possible set of scenarios with testing at this point. So the last option now is to replace the CAT. Its unlikely the issue is that the engine isn’t hot enough at this point, that has been tested.
What we need more than anything else right now is a very reliable garage that understands MX5’s has seen these cars of this age previously and can make sure we have the right problem-solution fit.
I will post another message in the forum to see if someone can recommend an appropriate garage to take it to.
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thanks for your response it is much appreciated!
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