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
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.
Who needs a life when you've got Unix? :-)
Email: firstname.lastname@example.org, John G.Burns B.Eng, Bonny Scotland
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?
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.
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.
*If you ate pasta and anti-pasta, would you still be hungry?
Dave Plowman email@example.com London SW
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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