840 Catalytic converters ruined by poor fuel (in UK) ??

I looked at an 840 the other day and the seller told me that he had had to fit new sets of catalytic converters. He said that BMW had told him that they die off because of the quality of the petrol.
I was suprised by this...
If this is true, is it because it's a car that's ~ 10 years old (although only ~ 50K on the clock) and petrol from yesteryear didn't have all the modern additives to keep the engine and cats clean?
So...this brings me onto a related question. What unleaded fuel should one run an 840 on? The normal or the "super" unleaded fuel?
Thanks everyone in advance
Griff
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Me too, BMW cats normally last three times that long.

Around 2000 we got ultra low sulphur fuel and that resolved one or two BMW issues. But I've never heard of it mentioned in the context of cats. And if it was a problem it'd be on all cars, not just BMWs.

Normal.
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Me too in the UK. It's as good as anywhere - and much better than most.
He's been listening to standard UK BMW dealerspeak. Ie, telling lies. They're all dreadful.
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Okay.....if they were "telling lies" then what would have been the truth? Why would the cats require replacing after so short a time?
Another thing. I asked earlier whether one should use the "normal" or "super" unleaded, and my thanks go to John for replying. I note though that several petrol companies are now selling "better performance & less poluting" NORMAL unleaded - an example is B.P.s "Ultimate unleaded". I presume that there are no draw-backs with using this petrol over "regular" normal unleaded (apart from the price). So, is this the one to go for for extended engine (& cat) life?
Griff
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The most common reason for the cats to have a premature death is from unburnt fuel getting into them. There may have been a rich condition (or may still be there) caused by a vaccum leak. My 98 740 had to have the cats replaced at 114,000 miles because of a leak about a year before.

Check your gas cap for a minimum. Again my 98 740 has the same engine and runs well on the BMW recommended 89 octane with an occasional tank of 92. I'm not sure what the marketing guys are calling all the different kinds of gas you guys have.
Kyle. 97 M3 98 740iL
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There's only really two in the UK. Premium which is 95(UK) is standard and near all cars are designed for it. Super is 97/8 and only a handful of exotics say it *must* be used - which is just as well because not all outlets stock it.
Of course these high octane petrols have fancy names and are heavily advertised since they cost more, but the advertisers are careful not to claim better performance or economy as they could be prosecuted under advertising regulations unless they could actually prove it.
I do use the high octane stuff on my 'other' car which dates from the days of 98 octane leaded and pinks on 95 as it has no knock sensors. Retarding the ignition to get round this results in poorer performance.
However, modern cylinder head designs and injection seem to allow as high a compression and ignition advance on the lower octane stuff.
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Kyle and Lori Greene wrote:

I don't get that one. If you have a vacuum leak you will have a "lean" condition, not rich. How do you think that would have cause the cats to expire prematurely?
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Depends on where the vacuum leak is. If in the fuel pressure regulator vacuum line (or effects it) this will cause the fuel pressure to increase and the car to run rich at other than full throttle.
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Dave Plowman (News) wrote:

Not if it is closed loop system with lambda feedback (O2 sensor), and I don't know of any cars with cats that don't have O2 sensors. Even with high fuel pressure the ECU should just cut back on the injector duration until the mixture was right.
My thoughts were that the more likely candidates for spewing raw fuel into the exhaust would be a bad O2 sensor (lying about the mixture), temperature sensor (telling ecu the engine is still cold) or problems with the ECU itself.
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It depends on over what range the 02 sensor can control the mixture - and remember under certain circumstances - full acceleration for example - the system goes open loop.

Indeed.
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Griff wrote:

Most likely the car had (or has) some sort of an engine management or ignition problem that caused excessive raw fuel to be exhausted into the cats. They can't take that sort of thing for too long.
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