4.8 - Performance Or Pia

[LVR]

Well went down to the dealer yesterday.... had the computer reloaded and still have detonation.

BMW AUST have said they don't know why it is doing it so it must be the fuel. I am wondering why the knock sensor doesn't eliminate it....

They have now asked me to only use BP Premium 98 RON as the other companies that supply fuel do not always meet this level.

Does anyone have any input or are using less than 98 RON unleaded in their 4.8?

Steve.. BMW are unable to obtain details of that bulletin. Any chance of getting an email address so that I can give my local dealer his contact?

[withidl]

I don't think your dealer has a clue! I assume your dealer's 98 RON means "Road Octane Number", not "Research Octane Number" (there is also a "Motor Octane Number). The 4.8 should be no different from the 4.4 on octane requirement. If your going to drive cross country it will have to operate on a minimum of 91 AKI (German for anti-knock index = octane) which your fuel door label should specify as my 4.4 does (in Oklahoma that’s the highest there is) and this is referring to the "Road Octane Number".

If you can't drive cross country what the hell good is the X5 to you? The knock sensors should retard the timing when they sense detonation to preclude it. I hazard a guess that your problem is either in your computer, your knock sensors or the wiring in between.

Additionally, ALL GASOLINE IS FUNGABLE. I worked for Texaco for 28 years so I know of what I speak. The petroleum companies exchange gasoline and diesel all across the country via the pipelines. If they didn't exchange the price of fuel would be so great you couldn't afford it and there would be constant supply interruptions. BP may load out of an Exxon terminal. The ONLY thing that makes a petroleum companies fuel unique is their advertising and proprietary additive which is injected at the loading rack of whatever terminal they may be pulling fuel from. The additives have nothing to do with the octane of the fuel. They are primarily to keep the vehicles fuel system and injectors clean and free of deposits. If you trade at any of the major oil company outlets you can be assured of getting a quality fuel.

[CJT]

I have done 15,000km in my 2004 4.8is now, and most of time I use Mobil premium which is 95 ron. I have tried the BP stuff at 98 ron, which is what I would prefer to use, but it's hard to get up here in the North.

I have never had detonation problems using the 95 ron.

I would never use normal unleaded at 91 ron, as that's right at the lower limit of what's required, and if you got a dud batch, then I'm sure the engine would let you know about it.

I just got back after driving 4000 km's in 5 days and used all different brands from Mobil's premium (95ron) to Caltex's (96.5ron) and she didn't miss a beat. Mileage was app. 13.5 litres to 100km which is great after my usual around town average of 21.

How long you have had the knock problem? - cause it does sound like a tank of dud petrol has come your way.

[LVR]

Thanks for the input guys.... it is appreciated.

The knock has been there for about 1 month. I use a variety of petrol sources as I get around a bit, however I AWLAYS use Premium, from whatever brand outlet I am at.

I have been through many tanks of fuel from different sources.

I know the fuel where I am has been criticised before because of its' "environmentally friendly" standards the local government has placed on it in relation to sulphur I think.

However, if it knocks, the sensor should retard it........ mind you, went for a blast down onto a freeway today.... the car seems slower since the re-program.

Not sure if it is me or maybe the knock sensor is now retarding it.......

[LVR]

Have spoken at length with 3 of the major brand fuel suppliers.

Caltex Anti Knock Index is apparently 91
Shell don't know what their's is....

BP have been very helpful with a number of questions and suggestions.....

It appears that the fuel here in Australia has been made lighter;

"January 2005 the National fuels
quality standards changed to restrict Final boiling point, aromatic
content and olefin content, essentially it has made the fuels lighter
but also eliminated some gas components that helped in combustion.
Where there are significant deposits on inlet valves then the lighter
fuels are absorbed onto the deposits and this can lead to knocking under
load until the deposits diminish."

They went on to state that stop start driving may be the cause of early deposit build up

"Certain driving styles contribute to engine
deposit build up, predominantly driving around city with lots of
cruising at 50-60 km then frequent stops and periods of hot soak
(typically called the real estate salesman mode of driving). If that is
the case then you may find an improvement from using Ultimate over the
next 5000 to 8000km due to its deposit removal additive."

and of course I happen to be in real estate....

Going to try a Carbon Clean before I do anything else, although the thought of having to do this after only 5000km's on the clock surprises me.

Has anyone had success with fuel cleaning additives?

[JCL]

The 98 RON in Oz refers to Research Octane Number, same as in Europe. The US pump octane (also known as anti-knock index, AKI) is the average of the Research Octane rating, and the Motor Octane rating. There are about 9 points between R and M, typically. 92 RON is approx the same as 87 pump octane in the US. 98 RON could be extrapolated to be approx 93 pump octane. So, for the OP, all those US posters running on 92/93 in the US are in approximately the same position as your 98 RON from BP. That is a big approximation, however.

There are many ways to get the pump octane rating, with higher or lower R and M numbers. So, the same fuels could have the same pump octane number, but different R and M numbers. An engine will respond differently to the R and M ratings, whether it is part load, or wide open throttle. Throw in the variations related to other items in the fuel, and it is very difficult to compare fuels between different geographic areas. the OP is seeing that with the change made to fuels in Australia as described by BP.

I agree with withidl about the US, here in Canada we have very few refineries and the fuel is the same for all intents and purposes. In other countries, however, the fuels can't really be compared. Best advice is to find one that works, and stay with it.

The advice I have for the OP is to be careful of carbon cleaning products, or, for that matter, any fuel additives. The only fuel additives I have ever used are injector cleaners (ie Techron, to fix sticking injectors) or stabilizers (for long term storage).

I would be relying heavily on the dealer to track this one down, in the belief that the knock sensor, or software, isn't right.

Good luck, let us know how it turns out.

Jeff