It would be interesting to know what would have happened had your original (non-scrapyard) cat been cleaned before the MOT using the soapy water bucket method.
Maybe I’m remembering incorrectly but I thought I saw people online using adapters to allow smaller cats on later cars due to a shortages a few years back.
It’s quite impressive how bad they look, yet still do the job required (mine’s the same in terms of looks).
Test Results
(new Aftermarket cat had been fitted 2938kms before
1st Fail:
Engine Oil Temp:80
Fast Idle
CO: 0.73% FAIL
HC: 60ppm PASS
Lambda: 1.010 PASS
Second Fast Idle
CO: 0.66%
HC: 41ppm
Lambda: 1.000
Natural Idle
CO: 0.34%
Second Test (Fuel Injectors removed, cleaned, refurbed, 279,274kms on them)
Engine Oil Temp: 60
Fast Idle
CO: 0.40% FAIL
HC: 37PPM PASS
Lambda: 1.020 PASS
Second Fast Idle
CO: 0.70% FAIL
HC: 62PPM
Lambda: 1:000
Natural Idle
CO: 1.73% (!!) Fail obviously
Third test; used factory 440mm cat fitted (unknown mileage, but the heatshield was rusted through)
Engine observed to be warm
Fast Idle
CO: 0.11% PASS
HC: 3ppm
Lambda: 1.0000
Natural Idle
CO: 0.48% PASS
This engine has “about” 100k miles on it, but all the peripherals are on 279k kms (engine was replaced at 200k kms, with replacement engine that had about 50k miles)
Original CAT sorted it then.
Not the original cat for this model. Original JDM cat was 375mm, changed to 440mm aftermarket, changed to scrapyard 440mm factory cat from a UK spec car.
Factory 440mm cats are no longer available.
Interesting my supercharged 1991 1.8 gets the same as that with no cats, obviously passes as it’s uses a pre cat check but when I look at the results they come out about 0.7/0.8%.
I’m fact it failed last year as they tested it as the wrong year.