92 to 95 emissions and CAT requirements, the answer (hopefully)

Technical Area Engine, Transmission, Exhaust etc
2

This will probably refer to Eunos Roadster imports and I will keep this as brief as possible, but it may be of interest and use to some on here.

There always seems to be questions regarding the requirement of a catalyst on some MX-5’s, typically early 90’s and imports, well hopefully I have the answer as far as current legislation goes.

My 1993 V Spec broke down some time ago. It was recovered by the AA and when I investigated it turned out to be the CAT had collapsed/broken up internally and blocked the exhaust, subsequently stopping the car. I took the CAT off, hooked out all the bits and refitted the empty shell and the car was fine.

When it went for MOT it had an advisory that the CAT was not working, but it passed the emissions test OK. On the next MOT this year it was again advised that the CAT was not working but it still passed. I asked the tester if I could fit a De-Cat pipe and he said it was a bit of a “grey area” as the manual stated that if fitted the CAT should be in place even though it only needed a Basic Two Gas test and not a full CAT test.

I decided to contact the VOSA help department to see if I could get any information, but was not confident of getting a reply. However to my surprise, I received a reply the next day giving me the current information. I have copied the reply below so that it may help others on here, but basically 92 to 95 vehicles only require a CAT test if there is a VDS identifying number in the emissions data available to the tester. This is taken from the 4th to the 9th digits of the VIN number. To me it would appear that NA6C and NA8C which are import numbers are not listed so do not need a CAT even if originally fitted.

Anyway a copy of the VOSA reply to me is below and will let you all inwardly digest and come to your own conclusions. Hopefully this will be of help and give a definitive answer. By following the inserted links the VDS codes and test data can be accessed. Any MOT testers on here with a view?

 

 

Hi Philip

 

There is no confusion.

 

Spark ignition cars first used on or after 1 August 1992 are subject to a Basic Emissions Test (BET) regardless of whether a catalytic converter is fitted or required.  In the event that the BET is failed, it becomes necessary to reference both the MOT Inspection Manual, Section 7.3 and the In Service Exhaust Emission Standards for Road Vehicles publication (Emissions book).  The MOT Inspection Manual is available on-line at http://www.motinfo.gov.uk/htdocs/ and the Emissions book at https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/194133/Emissions_17th_Edition.pdf

 

For vehicles first used between 1 August 1992 and 31 July 1995, if there is an exact match for the vehicle in the Emissions book, then a full cat test must be carried out.  Where this is the case, the vehicle must have a catalytic converter fitted or it will fail, regardless of the result of the emissions test.

 

If there is not an exact match in the Emissions book, then the vehicle will be subject to a non-cat emissions test (two gas test).  Where this is the case, the vehicle is not required to have a catalytic converter fitted for MOT purposes, regardless of whether one was originally fitted.

 

I am unable to provide an answer specific to a particular vehicle as you have not provided any details of such.  However, assuming you have the relevant Vehicle Identification Number (VIN), you can easily check for yourself using the link to the Emissions book and referencing page 70 of Section 1 (page 86 of the pdf).  The Mazda VDS number is the 4th to 9th digits of the VIN.

 

Regards

 

Technical Standards Team|

 

 

Testing Schemes Management

 

 

 

 

Incorporating the Driving Standards Agency and Vehicle and Operator Services Agency.

 

Find out more about government services at www.gov.uk/vosa

 

 

1 Like
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Yes, this agrees with what VOSA confirmed to me:  The MOT rule that MX-5s must have a cat and pass a cat test if they’re K-reg or newer only applies to imported Roadsters which are N-reg or newer.

I did find it necessary to print out the relevant pages from the documents VOSA mention, to show the MOT tester that i wasn’t making it up, and the tester still phoned VOSA for confirmation.  That advice got my L-reg Roadster through an MOT (although it still has its cat it would have been a marginal fail on fast idle CO).

4

Can anyone clarify where the two digits are on the end of this string NB18C2 as seen on the VDS listing ?
My log book confirms the NB18 but where is the C2 from ? New to me but reading up on this subject.

Thanks

5

The code is taken from the full 17 digit VIN.

Example: JMZ NB18C2 00 123456

6

I asked the question as my vin reads NB1862 so is that a misprint in which the 6 should be the letter C ?

7

The VIN will be on your car, why not have a look and see what it actually is.
:hearts:

8

I think that’s an oversight in the database. :shushing_face:

9

Well i’m back home and as i only had a photo file of my log book was unable to check the vin its so many years since ive had cause to do so. The vin is the same on the car, mine says NB1862 so it looks like as my car is not on the list mentioned it has to receive a basic emission test, would anyone agree ?
Technicality it may be but we can’t argue with our masters can we. It isn’t a match on the list so if it fails i can revert to citing the small print.

10

Technically every car has a BET first. If your car failed then that’s where the exact limits come into it and an NB could be a grey area. It has to be an “exact match”. Based on the age of the car, you won’t get off that lightly though.

11

According to the database, all NB and NBFL 1.6 are not listed. The NB 1.6 that is listed shows up as NB18C2 but according to this chart, the C is only used on the NA vin. All NB and NBFL use 6 for 1.6 and P for 1.8.

12

If a car’s first use was on or before 1st august 1992, then the BET test does not apply.

13

Yes sorry, any car that potentially needs a cat test has a BET test first.

14

All cars from K-reg on get a BET. Cars not listed in the database then get an extended test based on their age. Up to M-reg they get the lax non-cat test. Up to 02-reg they get a test that’s only fractionally less tight than the BET. Newer than that they get a test which uses the same values as the BET.

If you google ‘In Service Exhaust Emissions’ you can download the pdf of the current edition and there’s a table on page 10 showing the actual figures.

15

Thanks to everyone for their input. Most helpful.
The problem imo is your dealing with what is a very old designed engine only changed/upgraded with the edition of DOHC heads as we have and so asking it to perform as good as something ten or twenty years younger is the problem. Had my car getting on 12 years now and that has always been the stumbling block if any at mot time despite doing my best to keep it running correctly. If i cane the life out if it and get straight in its always gone through but as one mot tester said if i haven’t driven it like ive stolen it or its had time to cool then it only scrapes by.

16

Just replaced the timing belt etc and discovered that the garage whom replaced it in the past left the exhaust cam a tooth out timing wise and the belt slack in that between the timing marks at the 12 O clock position there were 20 teeth and the belt arched/slack.
So with the crank at tdc and the inlet cam correct the exhaust was a tooth or so further on rotation wise, not much but not correct.
Its always seemed ok starting and running but now i wonder would this have had any effect on the emission readings mot time ? Anyone experienced similar or have knowledge of the effects if any ?

17

Now that’s interesting. I have no experience to compare but I would not be surprised at all if the exhaust valves opening early would add more incompletely combusted material to the exhaust. Since the cams turn half as fast as the crank does, a one tooth advance in cam timing is a little over 15 degrees error in crank timing terms.

18

Thanks for your reply Martin, i won’t know for sure until mot time but the only thing i thought had changed was the cold start idle which i think has risen by a few hundred rpm. The car is off the road for winter now so i’ll be interested to see if it performs any different.
One thing though for which i have always believed in, never trust anyone else with your car if you can do the job yourself. Take your time and do it correctly if you have the necessary ability. Now i’m retired the time part is easy :grin:

19

A timely update to an old thread. My 1996 Roadster has been stuck in Thrussingtons, for over 2 months, following MOT fail for the usual high CO. Previously, whack on a cat. I’ve been through I think 3 cats in 5-6 years. The latest failure still has stickers on it.

This time around, Mike decided to try and get to the root of things, ie the continuous failures are a result of something wrong with the engine (an engine that has always pulled well, and gives decent MPG). The complication is the engine has around ~100k miles on it, but the bits that bolt onto it are more like 170k miles. He thought he had a eureka moment, by spotting a slight miss at a faat rpm, and hypothesized the 170k mile injectors might need a clean.

Cleaning the injectors turned into a 4 week marathon due to hospitalisations and an unrelated COVID outbreak. The contractor pronounced the injectors “not that bad”.

On went the cleaned injectors. CO improved a little and now the engine is beautifully smooth. But it still failed on high CO on fast idle. Everything else on the engine checks out, so we are back to aftermarket cats are not very good.

I thought I understood the MOT rules; I had somehow believed that my Roadster, although subject to a cat test was somehow held to a different (lesser) standard. The replies here and official documentation prove otherwise. Plus the MOT tester is insistant he is correctly following the rules by subjecting the car to a “1995 test”.

On 1 January 1996 a new test was introduced for petrol fuelled passenger cars fitted with advanced emissions control systems such as three way catalytic converters.
The test was extended to include large petrol fuelled passenger cars and petrol fuelled light goods vehicles from 1 August 1997.

The test applies to:

• Passenger cars (1) first used on or after 1 August 1992 and mentioned in the Annex to this publication.
• All passenger cars first used on or after 1 August 1995.(2)

(1) The Road Vehicles (Construction and Use) Regulations 1986 (as amended) define a passenger car as a motor vehicle which is:
a) constructed or adapted for use for the carriage of passengers and is not a goods vehicle;
b) has no more than five seats in addition to the driver’s seat and;
c) has a maximum gross weight not exceeding 2,500kg.

(2). Passenger cars first used before 1 August 1995, not mentioned in the Annex and which at date of engine manufacture were incapable of passing the catalyst test will be tested to non-catalyst standards.

Note the emphasis on “All passenger cars”. My misunderstanding is if the car (Eunos Roadster) wasn’t listed in the annex, it reverted to some other test standard. Not true.

On a N-reg car, the annex is irrelevant.

The Roadster in question has a 440mm cat. I’m now pinning my hopes on a fairly rancid looking factory UK spec 440mm cat from Autolinkuk (£250!!)

catalytic-convertor-mazda-mx-5-1.8-mk1-440mm-b6gp20600a-used-(3)-12605-p
catalytic-convertor-mazda-mx-5-1.8-mk1-440mm-b6gp20600a-used-(3)-12605-p2048×1436 219 KB

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With the cleaning injectors and scrapyard cat, my car flew through the MOT, with comments like “best emissions” seen in a long while “couldn’t get any better”. And better numbers than when they have previously fitted brand new aftermarket catalytic converter (to they extent they were expecting a top end rebuild in the near future). This voyage of discovery cost me £800+.

The aftermarket 440mm cats sold in this country appear to be basically junk, and the supply of used factory 440mm cats is limited and finite (one day there will be none).

Cars registered before August 1995 revert to manufacturer specified limits. August 1995 onwards I think, as I read it, use statutory limits.

Roadsters will struggle; all 1.8 Roadsters had 375mm cats, bu UK cars had 440mm and 475mm cats. The 440mm cats seem to be marginal, because of how poor the aftermarket replacements are. My Roadster is running a 440mm cat, but on top of that, was also first used in 1996.