Cat or no Cat? That is the Question

Technical Area Engine, Transmission, Exhaust etc
2

Can someone shed some light on this question?  I have a 1993 MK1 Eunos Roadster which iwas imported in 2002.  I have a MAC sheet dated 14/06/2002 and it was registered in the log book on 01/08/2002 - it was [:S]then given an age related plate as per end of December 1993 due to year of manufacture.  So does it need a cat to pass the mot or can it escape without one?  I have not climbed under the car yet to determine if it is a cat or a bypass pipe.

Any suggestions greatfully welcomed.

 [:S]

3

 Date of manufacture sir… Its all good, De-Cat,
Alex [H]

4

 
 
+1, as confirmed by the Mazda dealer on my recent MOT…different emmissions test or something…

5

This was written by an MOT tester and Mx5 spanner god

Vehicles presented for test that were first used between August 1st 1986 and July 31st 1992 will be subjected to a Non Cat. Test. This test applies the limits of 3.5% Carbon Monoxide (CO) concentration and 1200 parts per million (ppm) hydrocarbons (HC).

Any MX-5/Roadster with a fully functioning, well maintained engine management system with the engine at normal operating temperature will be able to meet these limits even with a decat pipe fitted.

Any vehicle presented for test that was first used on or after 1st August 1992 will be initially given a Basic Emission Test (BET). The emission limits set down for this test are a Carbon Monoxide concentration of 0.2%, a maximum Hydrocarbon concentration of less than 200ppm and Lambda must be between 0.97 and 1.03 at a fast idle speed of  between 2500 – 3000rpm (fast idle). Then at a natural idle speed of between 450 and 1500rpm (natural idle) the CO% must be 0.2% or less.

 

Any MX-5/Roadster with a fully functioning, well maintained engine management system with the engine and catalyst at normal operating temperature will be able to meet these limits.

 

If for one reason or another, your vehicle fails the BET, then the tester will follow a number of set procedures.

  

  1. If your car was first used between August 1st 1992 and July 31st 1995, then the tester must look for an exact match in the Service Emissions Book. This book lists every model of vehicle and states the emission limits for each vehicle. In the case of MX-5’s the limits for vehicles of this age is 0.3% CO & 200ppm HC at fast idle and 0.5% CO at natural idle.
 

By design, an MX-5 of this age with its catalyst removed will not pass this test

 

  1. If an exact match can’t be found, as is the case for Eunos Roadsters as these are not listed in the Service Emissions Book, then the tester re-tests the vehicle applying the limits of CO at 3.5% or less and HC at 1200ppm or less at natural idle, a non cat test.
 

A Roadster with a fully functioning, well maintained engine management system with the engine at normal operating temperature will be able to meet these limits even with a decat pipe fitted.

 

  1. If your car was first used between August 1st 1995 & August 31st 2002 then again the tester must try and find an exact match in the Service Emissions Book. MX-5’s are listed and must meet the emission limits of less than 0.3% CO and under 200ppm HC at fast idle and 0.5% or less CO concentration at natural idle. Roadsters of this age, not being listed in the book are now subjected to a CAT test using default limits of 0.3% CO or less, HC 200ppm or less and a lambda reading of 0.97 to 1.03 at fast idle and a CO reading of 0.5% or less at natural idle.

By design, an MX-5 or Roadster of this age with its catalyst removed, will not pass this test.

All vehicles first used on or after September 1st 2002 are tested to vehicle specific limits if an exact match can be found. A CAT test using default limits is carried out where an exact match can not be found.

This information was correct as of November 24th 2008. MOT regulations are constantly changing so it’s accuracy can’t be guaranteed for any period of time. The emissions levels change for different vehicles this info is specifically for Mazda MX-5 or Roadster and Eunos Roadster.

Errors and omissions expected and accepted but the info is correct to the best of my knowledge.

 

 

6

So let me get this right before I go and spend £50 and the time fitting it…

I have a 1994 roadster 1.8 emissions at present are Co 0.06% and HC 49ppm at idle. & Co 0.04% and HC 36ppm at 2566 rpm.

If I fit a silenced Decat, my car will be classed as a car not listed in there book, so they will compare it to a pre 1992 car. and therefore should pass the emissions test with flying colours???

Is that right???

7

Close!! Your car is not an Mx-5 so has no listing wether it has a cat or not. It therefore defaults to unlisted (No2 in Red)

8

 
Richardn you need to take a chill pill.

9

[H] Just telling it as it is [H]

10

Thanks Richardn for helping me clarify that. Can’t wait until I get one and fit it!!!

P. S. Isn’t it funny this emailin thing, some people can interpret what you say completly differently and and take offence???

11

I fitted the MX5 Parts de-cat pipe onto my '89 Eunos 2 years ago. It’s passed its MOT both times since, but I have to be honest, I couldn’t tell any difference in sound or performance. It already had an aftermarket exhaust fitted anyways, but i still initially thought it would make a slight difference. Hey ho, at least it was a lot shinier than the old cat it replaced hehe

12

Well got my de cat today and had it fitted £15 at the local Wilco’s. Now I might have to agree with you there…

The sound doesnt sound that much louder if at all. Maybe a bit more burblely at the lower end of the rev range, and it has made my idle, and general ride appear alot smoother. Will have to report back once its bedded in.

13

Interesting that Wilco’s fitted it for you, my local Wilco in Lynn wouldn’t do anything to the exhaust that they didn’t supply themselves.

14

Could not get the bypass pipe fitted for some reason. I will speak to MX5 parts to see if I did something wrong or it was the wrong part. It fouled a bracing piece of metal below the propshaft. However have fitted the twin exhausts from MX5 parts and they look superb and sound awesome. Just the K&N to go on now…

15

Had my decat on for about 2 weeks now - awesome - love it.  lovely burble.  Had the timing done at the same time.  So smooth through the revs.  K&N been on a week.

16

I think the wilco man did as they were board and didn’t look to busy… Cash in Hand (nudge nudge wink wink)

I asked at a couple of large garages and they wouldn’t do anything if they hadn’t supplied the part.