my car failed emissions,

Hello, i am new on the forum, I have a 1998 car who has failed mot, for emissions, I did run it hard, it was warm, The previous owner had the same problem,  He replaced the cat, the oxygen sensor and never returned for mot,  I went with the replaced cat and sensor , But it failed again, After that attemed, i replaced a worn out cap and rotor, and i waited to get my pscan tool.  It does not give me any error codes, I have some live data but it is all new to me and  i need some advice,  can the worn cap and rotor  be the problem ? yes , but is there anything wrong with the live data ?  i cant drive the car to any specialist, it isnt allowed on the road yet, problem is , It needs mot to get it on the road. Any mg specialist is a long ride  and i dont take that risk yet.  If everything seems to be ok on the readings i might swap for a new cat ,  or just retry mot because of the new Cap plugs and rotor? the cap and rotor  looked real bad, but the car never missed and it pulled strong. the pluges looked ok, but i replaced them anyway. Any help would be apriciated.  

Gday and welcome to the Tbar, May I suggest you have a look at this checklist for new members: https://www.the-t-bar.com/forum/54-how-tos/99326-a-check-list-for-new-owners
It won't help much with your current predicament by youmay get something out of it. Now I'm in Australia and my state doesn't do annual RWCs (MOTs) or emission tests so I'm not the bloke to ask about passing you MOT, but I'm sure someone will be along shortly to help.

thanks, i have the car for almost 6 months, i read a lot about it, replaced a lot, like all fluids and tires, also fitted a coolant level alarm, it is in real good shape, new exhaust system, coolant tubes, belts, it is rerady for the road , if it passes the emissions, they test it at 2500 rpm and i think it had 0.9 and it has to be 0.5 i guess, but i am not sure of that ,

Hi and welcome. 
You say that you have replaced the cat, was it with a type approved one? Some of the cheaper ones are very poor quality and don't perform as well as the original part. 
Also it won't hurt to give the car a good service, air filter, plugs, cap and rotor arm.
Good luck and hope you get it sorted. 

Do you have readings from the MoT test on emissions and on what car failed? That is the most important thing as it shows where to look.

no info, they just say it failed on paper, the last attempt i had to run the engine steady at 2500 rpm and it was failed. i think it was 0.9 and it needed to be 0.5 or lower.
anyway, i replaced cap, and rotor, have ordered new sparkplugcables , plugs , and i ordered a new cat . the previous owner replaced a broken cat with a second hand cat, i think this wil fix my problem as nobody replyed on the little video i posted , i think all numbers are ok  but i am not sure. i hoped to see a faultcode , but i erased all old faults and no new codes pop up,  the pscan tool wa

Interesting.
I watched my MOT being conducted by the tester and started to become worried as it took a while to get the necessary pass for the exhaust aspect.

At the end I asked why he had so much trouble. The answer was as follows. For modern cars they can plug in their equipment to the OBD port but the port on the TF doesn’t join their “stuff”.
So they have to manually control the rpm and hold them steady for the required time period.
With the engine at the back and sticking throttle at low openings made holding steady rpm hard and it would have been easy to fail it on lambda/exhaust.
Has anyone else had this sort of issue?

I see the oxygen sensor voltage varying (so not stuck at one voltage), which is good.
I see the mixture control in closed loop control, which is good.

These are the obvious thing that I would look for, but they look good, so I can't really help beyond that.

Re#216325
I omitted to sat that with the MOT test centre using their equipment plugged into the ODB port I got the impression rightly or wrongly that their equipment controlled the throttle/rpm for the test. Don’t know how true that is but if true and the ODB in the MG is effectively non compliant then doing it manually will require a lot of patience and steady control on the throttle. Any variation and the test pass will not be achieved. So n unsteady throttle is bound to make lambda jump all over the place.
Might be worth asking if the test centre had ny difficulty doing the test (not what the result was).

Perhaps a go to a tester that knows these cars instead of some rando

I’ve been using the same test centre for the last fifteen years. The relationship I’ve built up is worth a fortune. I always arrange the first test of the day & although the MOT centre is five miles away it’s a fifteen mile hard drive to get there.
An hour the previous evening is taken up with checking those things that are “user serviceable” & if all is well I can sleep well.
As there are aspects of my car which differ from standard, I have to spend ten minutes to show the guys this years crop of modifications.
In a corrupt way it’s all quite enjoyable.
M