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Old 25th July 2022, 15:45   #1
Costa Fortuna
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Default Exhaust system original 2.0 V6

So I think I have the cat rattle feature - whilst changing the oil I decided to investigate the noise.

I'm pretty sure it is the cat because a tap with the end of a lump hammer handle produces a sound like there is something loose.

But here's the thing - working from the rear of the car there is the large box under the boot floor, a joint just rear of the axle line and then that's it - no more joins until the headers. There is a triangular box where the rear seat passengers feet would be, another round one under the centre console, then about 9" in front of that another circular box, then a flexi (which is a concertina type not woven), the cat then up to the manifolds.

There does not appear to be a downstream sensor just one on each downpipe. So how does that work?

Must surely be the original from the factory what with only one joint - I would safely assume the rear box has been changed at some point.

The car is a 2000 flavour manual.

At some stage this cat is going to need replacing - aftermarket ones seem to show a downstream sensor hole and just look different generally and Rimmers looks about right in their illustration but the aftermarket replacement looks the same as the ones available on the on the interweb.

Any advice/previous experience shared would be gratefully received, many thanks in advance.

Last edited by Costa Fortuna; 25th July 2022 at 15:58.. Reason: Re wording and general editing
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Old 26th July 2022, 14:21   #2
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i doubt that it is the original system. it should be stainless. second it would have three 02 sensors. third. the two cats would have been stamped and numbered. fourth the original would have the woven mesh flexi. the clamshell back box has already been changed by the sound of it. but i would suspect that it has had a cheaper all in one system fitted without the third post cat o2 sensor. that would have been inline approx with the rear lower engine mount. it may be plugged off with a bolt or was never there. if the wiring for this has been doctored or looped in , you would need to see underneath. all sounds a bit strange to me ...
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Old 26th July 2022, 14:37   #3
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The original system was indeed a one piece all the way through. the triangular shaped box is another give away of an original set up. My 2.5 KV6 launch model only has two sensors but others do have three. It isnt a problem, just plug the hole with an old sensor and cut the wire off or use another suitable plug. when retaining the original cat and purchasing the center section only, you had to lower the exhaust and cut it in the right place ( first time) to then join it onto the back of the cat.
So, if you can get hold of an original cat don't worry if it has two or three sensors unless yours actually has three. As I understand it all aftermarket ones have three sensor points but as said if your car only has two blank one off
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Old 26th July 2022, 15:01   #4
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well thats very interesting to know. thanks. i had assumed the 2.0 litre KV6 were all the same in design as my 2.5. live and learn .. hence my post. was there any reason for the lack of the third o2 sensor ? was it to pull in line with OBD emmisions updates of standards ? , as i would not have thought budget restrictions on early 2000 year were being considered not too far after launch.
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Old 26th July 2022, 17:03   #5
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Thanks Stocktake, there is no doubt that the system was factory fit, still there with no problems (apart from rattling!) after 22 years. The car hasn't been messed with at all and it's definitely a two sensor system all one piece to the rear axle line.

My question was more about fitting a new assembly - seems that the Rimmers illustration type has been binned for an aftermarket type which looks quite different - possibly has a sensor hole to plug and to cut and sleeve to the rest of the system. The fitting kit seems to cover what's required.

Still not sure about only having two sensors but relieved to hear that it is normal for these cars.

Part ordered should be with me tomorrow for me to fit ready for my 400 mile round trip to the Festival of The Unexceptional this weekend.
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Old 26th July 2022, 18:32   #6
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Quote:
Originally Posted by xsport View Post
was there any reason for the lack of the third o2 sensor ? was it to pull in line with OBD emmisions updates of standards ? , as i would not have thought budget restrictions on early 2000 year were being considered not too far after launch.
Haven't got a clue Stefan
My 2.5 Kv6 is early and no third sensor, when I needed a new cat ( rattle rattle ) I visited a breakers yard ( those were the days) and nabbed one off a X reg IIRC
To this day I have a lamda sensor in the third hole , (Oooo missus,) with the wires removed.
Now, remember to keep your clips apart
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Old 26th July 2022, 21:04   #7
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i suspect a second sprat to catch a mackerel is afoot !!
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Old 26th July 2022, 21:05   #8
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i will certainly be paying attention. ..
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Old 27th July 2022, 07:33   #9
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Default KV6 year 2000

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Originally Posted by Costa Fortuna View Post
There does not appear to be a downstream sensor just one on each downpipe. So how does that work?
Here's an extract from a 1999 RAVE document Tim:

"There are two oxygen sensors fitted to a Rover 75 which utilises a Siemens 2000 EMS, both are pre catalyst. There is an option for a third (post catalyst) when the EOBD regulations are implemented during the year 2000. The pre catalyst sensors are located in the downpipes (one for each bank."

So on your car, Stocktake's and mine, the two sensors are used to ensure that the air to fuel ratio is correct by monitoring the exhaust gases but catalytic converter operation is not included (except at MOT test time).

As your exhaust system appears to be original (except for the back box), if it passes its MOT I wouldn't worry about the rattle. Aftermarket catalytic converters are nowhere near as good as the factory item (from experience with my other car). Leave well alone!

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Old 27th July 2022, 09:57   #10
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I would, Simon, but you can hear the thing rattling coming down the street as I found out recently when my wife borrowed the car

Short of a bodge whereby I introduce long screws or suchlike into the casing which I'm really not keen on doing because it may cause more damage to the core replacing it has to be an option.

Shame because I like to keep things stock if I can but the original set up isn't around anymore it would seem and even if I did find a NOS one I would end paying far more for it than I paid for the car.
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