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  #1  
Old 10-11-2011, 03:18 PM
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Gas Octane for my 2008 3.0si

Hi -

I know our X5 requires a minimum of 91 Octane but when I filled my tank with 91 Octane as oppose to 93 Octane, I noticed a knocking/pinging sound from the engine. I don't know if that was a coincidence or if it's something else. Has anyone here have this problem? Thanks.

Kiet
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Old 10-11-2011, 03:43 PM
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You shouldn't hear any knocking or pinging from the fuel, as the engine management system will take care of that.

If the fuel was really bad, that could cause it. Not just lower octane rating, but water or other contaminants. You don't really know that it was 91, just that it said 91 on the pump. Try a different station if it continues.
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Old 10-11-2011, 05:42 PM
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There are knocking issues that have been well documented that do not stem from the fuel.
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Old 10-11-2011, 07:04 PM
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I had the same issue regardless of what fuel I used. It was the lifters that had to be replaced under warranty.
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Old 10-13-2011, 03:26 PM
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Thanks guys for the response. I checked a couple of more cold starts and do not hear the knocking sounds any more. I was going to bring it to the dealership to have them take a look but no longer hear that pinging noise. I think I will hold off until it comes back again.
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Old 10-14-2011, 01:19 AM
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A properly functioning X5 will NEVER exhibit 'pinging' or 'knocking' due to low octane, even down to 87 .

It is important to be precise when using those terms as they can be misleading. (In your last post you flip flop with the terms- if you bring that to the dealer, they will not have any idea what you are talking about....Be as descriptive as you can, the more descriptive the better.

What brand of fuel? Any reason to suspect an issue with that fuel over than the labeled octane?
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Old 10-22-2011, 03:07 AM
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If the fuel quality is bad enough, and under particular load conditions, there is certainly the propensity for it to knock or ping. The knock sensors will retard timing to a safe level until it is gone. However, going from 93 to 91 explains this as the DME will advance timing on it's own. When you went back to 91, it was expecting higher quality fuel and thus there was too much timing advance.

I'd always run 93 if it was available here!

And if you put 87 in it, you better believe it's going to ping. There is fallback programming for low octane fuel as well as low / hi octane maps in the DME.
The pinging noise has probably gone away because it has re adapted to the poorer fuel quality. These cars have extremely sophisticated engine management systems.
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Old 10-22-2011, 05:31 PM
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Never heard any pinging on any recent BMW, on 87 or 89. The DME is operating at the speed of sound; there isn't an adaptation period in my experience.
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Old 10-22-2011, 05:37 PM
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Quote:
Originally Posted by JCL View Post
Never heard any pinging on any recent BMW, on 87 or 89. The DME is operating at the speed of sound; there isn't an adaptation period in my experience.
Do you tune ECU's?

Do you know how minimum ignition maps work on this particular DME family?

Do you know about target based systems, and how this works in conjunction with minimum timing maps when you change the targeted timing?

I wouldn't make statements that the "DME is operating at the speed of sound" when that is not of relevance in this particular case. I could go into processor architecture here, but that's a whole different case. And were talking about faster than the speed of sound.. these are electrical signals.

There are so many different adaptations - over 20 of them. Do you think that the DME can pull timing infinitely? It can't. It will to a certain point.

If you go from higher octane to lower octane, there is a chance it will ping until it makes corrections to prevent it from happening.

On some E46 M3's we REMOVE timing from stock in certain areas due to the factory timing maps being too far advanced in certain areas for 91 octane piss water fuel.
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Old 10-22-2011, 05:37 PM
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Quote:
Originally Posted by JCL View Post
Never heard any pinging on any recent BMW, on 87 or 89. The DME is operating at the speed of sound; there isn't an adaptation period in my experience.
+1...I've run tanks full of 87 & 89 through our '01, in the past decade; never an unusual sound or 'detonation', and also no discernible difference in 'performance'.
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