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[paul8594]

Hello everybody,

silly question time.

I have a V reg 3.0 elite estate which i have replaced both CATS and LAMBDA sensors (which i have to admit not with main dealer parts.)

The exhaust sounds like its blowing, had this checked out and its not but it was noted that the cats were running "red hot"

The MPG has gone right down around town to 20.7.

When i fitted these i noticed that they looked a lot smaller tha the original ones i took off, i rechecked the paperwork that came with them and they are marked as being for my vehicle

The silly question is, can a CAT cause these problems and is there such a thing as a too small cat?

Thanks

[Broomies Mate]

If you are restricting the flow of exhaust (as all cats do) then you are causing lots of back pressure.  Excellent for Turbo'd engines, really bad to NA engines.

Aftermarket cats are useless rubbish.  That said, all cats run 'red hot' (as long as they arent actually glowing red, lol).

Feel both tail pipes, and see if you have equal pressure from each.

[aaronjb]

The lambda sensors you replaced, were they the ones before the CATs or after?

If they're before and you're now getting terrible fuel economy and the CATs are over temperature, then I'd suggest they might be causing overfuelling..

(Though, yes, operating temperature of a CAT is .. hot! and the output gasses should be hotter than the input gasses)

[Andy B]

The lambda sensors you replaced, were they the ones before the CATs or after?  .....

None DBW cars only have 1 lambda per side & it's after the cat     

[aaronjb]

Ahh.. whoops, I assumed they were all OBD-II style with pre & post-CAT O2s

I'll just be over here in the corner with my pointy hat on

[Broomies Mate]

To be fair, being a 'V' plate, we dont know if it is Facelift or Pre-Facelift.

[Andy B]

To be fair, being a 'V' plate, we dont know if it is Facelift or Pre-Facelift.

facelift or prefacelift .... it makes no difference. All 3.0 & 2.5 cars have a throttle cable, it's 3.2 & 2.6 cars that are DBW 

[Broomies Mate]

To be fair, being a 'V' plate, we dont know if it is Facelift or Pre-Facelift.

facelift or prefacelift .... it makes no difference. All 3.0 & 2.5 cars have a throttle cable, it's 3.2 & 2.6 cars that are DBW 

You are so right.  Sorry Andy, I'm half asleep and thinking about sheep jumping over fences.   

[amba]

Against my better judgement and more  of a urgent necessity I opted for a replacement nearside cat for my Elite just after Christmas this year.

Can honestly say it was the worst money I have spent for ages.The car sounds like a boy racer when inside so who knows what it must be like from outside.The actual cat is about 1/3rd the size of the original part and that which is still on the offside exaust.I doubt if it would last too long as must be a very thin gauge metal.

I have gone back to the supplier several times to complain but they tell me they are all like that now and even if they replaced it again it would be no different.Out of desperation I have sourced a genuine GM cat from a breaker with 80k,s worth of use and am awaiting its arrival in the next few days.

Hopefully it will quiten the car down and then all I will hear is the noise from the nearside exhaust manifold gasket blowing which is getting further up my list of jobs that must be done before winter.