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MG MGF Technical - High CO, Low HC - MOT

Pre-2000 MGF VVC

I have just had my car MOT'd.. and the good news is, it passed.

The bad news is that although the HC level was well below any limits (32 ppm vol)..,
the CO level was bang on the limit (0.30% vol)

I'm thinking Cat or Oxygen sensor.
Any advice?

I believe it must me the Cat else wouldn't the CO levels vary a lot? (i.e. go up and down)?

Is it cheap/easy to change.

P.S. Before anyone says it.., I don't need Cataclean!! LOL.


Neil H

Prolly neither, do you know for certain that the cat was very hot when the did the test, some garages stick the sensor in and wait for it to come into range, so you will always see a 'top of scale' reading. The MOT place generally use an oil temp sensor to work out how hot the engine is, on newer car design the cat is put closer to the engine so it warms up faster - they may just be used to newer cars.

In answer to your question No and No for the cat and probebly not and probebly not for the sensor.

Will
Will Munns

Ooo! I don't know.

The guy is a friendly enthusiastic mechanic that I've never used before.

He did the MOT and I wouldn't be surprised if he knew nothing about MGF's.

He said it took a few goes to get it to pass, but he was warning me that there was probably no way I could get through next year.. - hence I thought an investigation was in order.

Probably doesn't tell you much, but I drove the car on a motorway journey.., and he tested it about an hour later.

Anything I can check on the car to access the state of everything?
Neil H

not really, you could test the lamda sensor was reacting fast enough (as they get old they switch slower), but you'd preobebly need an oscilliscope to do it.
Will Munns

D'oh..

So your recommendation would be to ignore it and deal with it next year 'if' there is a problem?

Neil H

Will.. I have just had another thought.. ;- The idle speed was 886rpm. Does that suggest the car was slightly cold??

What is the normal idle rate (800?).
Neil H

Idle rpm varies between 850 and 900 as far as I know, so 886 is good enough

Johan
Johan Slagter

This thread was discussed on 22/07/2004

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