What can I do?

Not quite correct. It’s not regardless of the emissions regs it must meet.

A car will fail if it’s inspected for the presence of a factory-fitted cat and the cat ain’t there, but the MOT tester’s manual says “This inspection is only for vehicles that must have a full catalyst emissions test”.

Your 1991 car pre-dates the requirement for a cat test, so it doesn’t get inspected to see if a cat it there.

1 Like

Hi I have a 1992 Eunos and the original cat failed so I bought one from MX5 parts it failed within weeks and started rattling in the end believe it or not I called kwik fit and they were able to supply and fit a much better quality one which even had the sensor fittings on it which the one from MX5 parts didn’t have,3 or 4 years later still working fine the only thing none of them have is the heat shied, I have always been told by the mot people that if it was built late 1992 or later it had to have the cat fitted

Cheers gordon

Hi Pollyanna,
You have possible causes to your cat failure which need to be sorted first before renewing your cat.
You say it is making a rattling noise.

  1. Damage to cat caused by striking cat on road causing monolith inside cat to break loose.
    2.Faulty or poorly made cat where monolith has broken loose inside casing.
    3.The most probable cause is misfire on engine (I.E faulty plug or plug lead) causing excess fuel to enter cat which results in extreme temperature being created inside cat resulting in monolith melting thus causing a rattling sound as it moves around inside casing.
    If cat is removed from car & you look through the cat you should only be able to see a slight amount of light shining through,(the light is coming through fine tubes as the monolith of the cat when removed is a very fine honeycomb)
    If you see a small piece of the monolith moving around it has more than likely melted due to excess heat & any warranty will be rejected.
    Remember your rattling cat could be a result of a problem not a cause, so the cause will need to be found first or you could have another cat failure if you just replace it.
    Other possibilities could be faulty oxygen sensor or temperature sensor telling ECU engine is cold & telling it to richen fuel mix but that problem usually shows up with a non or poor start up when engine is warm.
    I have personally had a non faulty cheap cat return a emissions reading of 0.32 (Fail) on my 1.8IS,when original cat fitted back to car (new one was fitted so i could repair heatshield on old unit) it resulted in 0.01(Pass) even though it was 23 years old.Unfortunately most aftermarket units are not of the same quality as an original manufacturers unit.
    As stated by other members your vehicle will have a emissions test with a max reading of 3.5% for a pass.
    Hopes this helps

Hi gentlemen. I have purchased what seams to be a decent catalytic converter from MX5Bitz and I want to have the car engine etc checked to make sure it is performing properly before the new cat. is fitted. Could some one with a lot of knowledge about the Eunos give me some good info that I can ask my garage man to do BEFORE he fits the new catalytic converter? In language an old man can understand if possible please. I am going to ask the garage guy to give me something written down about what he has done before he fitted the new cat, so that if anything goes wrong with this cat i have written evidence of what was checked before fitting cat

Check plugs, ignition leads, coil pack, O2 (lambda) sensor. Maybe put some injector cleaner through. Check the cat for external damage; some of the aftermarket ones hang very low.

As a slight aside. If you have a genuine OE cat then check the code before you chuck it in the recycle bin or let your exhaust man ‘dispose’ of it for you. Scrap value working or not could be £250-£650.

Thanks for the info saz9961, I will on Monday be going to see the garage mechanic to show him all the info that you have given me plus a bit of extra info that came with the cat. After it has all been done and hopefully passes its MOT this time, I will let you know how I got on.

There’s a bedding-in procedure for new cats to ensure they last, it might differ for some but here’s an example:

“To start the break-in procedure, start the car after you’ve replaced the cat. Let the car idle in place without applying any gas. When the engine warms up to its operating temperature, get inside and give the car enough gas to bump the RPMs to around 2500. Hold it there for 2 minutes and then release the gas. Shut the car off and let it cool down completely.”

Thank you for that information, I will see that it is done after the car has its diagnostic check done, the cat fitted and its passed its MOT.

I think what carl_s is saying is that you’ll need to do the bedding in of the new cat immediately after it’s fitted. Let it cool then do the MoT.

I suppose the garage will run the car up to temperature after fitting the garage and checking for leaks etc.

Hello everyone. As I promised to let you all know what happened about my MOT and CAT problem, here it is. I bought the new Catalytic Converter from MX5BITZ, they were very efficient in getting it too me, and also checked with my registration that I had ordered the correct item. I took it to the garage who had failed it last time and let them know that I had found a CAT that I thought was the best I could get hold of and were they prepared to do a full diagnostic of the engine, fit it and then MOT it. “No trouble they said, bring it in at 9.00am in three days time and it will be done”. All went smoothly and it passed its test ok and to my surprise the whole exercise cost only £85.00.
The garage concerned is Auto Test 84A High Street, Northallerton, North Yorkshire. Phone no 01609 777151 In case there is anyone who is interested in having a good job done at very fair prices. This
is not a Rip Off merchant, they will tell you when there is anything that will need to be looked at in the future or before the next MOT. Not like a Main Dealership who would do the work and charge you even though it didn’t really needed doing at the time. I have had this happen to me in the past, never again. As far as I know they also did the warm up part of fitting the CAT.


Today, Saturday 28th, I just realised that after having the new Catt fitted the garage mechanic very kindly put the old one in the boot, so if time allows tomorrow I am going to cut away part of the outside body see what it is like inside. If it looks interesting I will try to find out how to put some pictures of it on here for anyone who is interested to have a look at.

It its a factory original cat, its worth a fair bit of money scrap. Must be pictures of cats cutaway on the web. Plus I suspect you would be exposing yoursef to a lot of carcinogens.

Just a crumbly honey comb

That is interesting, I won’t bother to cut into mine to see what it is like. How should I dispose of it as it was only one of those cheep ones from MX5 Parts so i don’t suppose it will be worth anything?
Noting the time you replied to my comments it looks like you don’t sleep very well either.

A long shot probably, it could be worth firing off an email to Mx5parts saying how poor their cats are. Still have the receipt?

Nothing ventured…and all that.

1 Like

It puzzles me how cheap aftermarket cats can be. With many OE ones worth up to £600 scrap value, they must be cutting corners somewhere?

Many mk 2/2.5 have had their cats stolen. In many cases the cat alone is worth more than some complete cars are selling for.

In my opinion the cutting of corners is done by reducing the size of the cat which is made of precious metals.

Look at the size of an OE NB cat compared to an aftermarket one.

Because we don’t want to pay £600 a cat.

What precious metals are they made of?